OPINION OF THE COURT
Appellant Charter Oak Fire Insurance Co. (“Charter Oak”) appeals the order of the district court entering judgment in favor of appellee Sumitomo Marine and Fire Insurance Co. (“Sumitomo”). Charter Oak, appellant in this case, insured John D. Wodarski and Wodarski Sled and Cycle Shak, and Sumitomo, appellee, insured Yamaha Motor Co. Charter Oak settled a judgment against its insured in a state court action in which Raymond Peterson sued Wodarski and Yamaha for damages resulting from a snowmobile accident. In this diversity case Charter Oak asserts that Sumitomo wrongfully failed to defend it in the action and indemnify it for the amount paid in settlement. The district court conducted a bench trial in the case and entered an order dis*269missing Charter Oak’s action on the basis of collateral estoppel.
Peterson sued Wodarski, an authorized dealer in products designed and manufactured by Yamaha, and Yamaha, in the Common Pleas Court of Erie County, Pennsylvania for injuries sustained by him while operating a snowmobile manufactured by Yamaha and sold to him by Wodarski. Peterson asserted both a negligence claim and a strict liability claim, alleging that the snowmobile had a defective throttle mechanism.
Yamaha was insured under a comprehensive general liability policy containing a broad form vendor’s endorsement, issued by Sumitomo, and Sumitomo retained counsel and managed Yamaha’s defense. Similarly, Charter Oak and its counsel controlled Wodarski’s defense. The same counsel represent Sumitomo and Charter Oak in this action. In the state action, counsel for Wodarski answered Peterson’s complaint and included New Matter under Pa.R.C.P. 2252(d), joining Yamaha in the nature of a cross-claim for contribution and/or indemnity. In the cross-claim Wodarski asserted that if it was held liable to Peterson by reason of selling a defective snowmobile, then Yamaha was liable to it for all damages, and costs of defense. App. at 402. In this federal court diversity action, Charter Oak again claims reimbursement and indemnity, this time from Sumitomo alone, rather than from Sumitomo through its insured, Yamaha. In addition, Charter Oak asks for damages arising from Sumitomo’s failure to defend it in the state court action.1
At the conclusion of all testimony in the state court litigation, the court of common pleas directed a verdict for Yamaha against Peterson in the underlying tort action and for Yamaha against Wodarski in the cross-claim for indemnity and defense. After a six-day trial, the jury returned a verdict for Peterson against Wodarski for $250,000.00. Wodarski filed post-trial motions contesting both the jury verdict against it and the dismissal of its cross-claim. After the state court denied the motions, Wodarski appealed, then settled with Peterson and withdrew its appeal.
The record clearly indicates the reasons for the various dispositions in the state court action. The evidence showed that the snowmobile came from Yamaha in an undefective condition and that while it was in Wodarski’s possession and control; persons employed by Wodarski took apart the throttle and then improperly reassembled it. The jury’s verdict against Wodarski necessarily rested on a finding that the misassembly caused the throttle to stick and that the sticking of the throttle caused the accident, since this was the only theory of liability presented.
The insurance policy between Sumitomo and Yamaha contained a vendor’s endorsement which excluded coverage for “(b) bodily injury or property damage arising out of (i) any physical or chemical change in the form of the product made intentionally by the vendor, or (ii) demonstration, installation, servicing or repair operations, except *270such operations performed at the vendor’s premises in connection with the sale.” App. at 20. Charter Oak bases this action for indemnity on the vendor’s endorsement, which was available to it during the state trial.
The district court properly dismissed Charter Oak’s claim under section (b)(i) of the vendor’s endorsement. In its pretrial submissions, Charter Oak admits that the injury did not occur during a demonstration, servicing or repair in connection with the sale of the snowmobile. App. at 144. The district court likewise correctly concluded that application of finality of judgments principles precludes appellant from claiming in federal court that it is covered at all under the vendor’s endorsement.
The law has developed the doctrines of collateral estoppel and res judicata in order to “protect ... adversaries from the expense and vexation attending multiple lawsuits, conserve judicial resources, and foster reliance on judicial action by minimizing the possibility of inconsistent decisions.” Montana v. United States, 440 U.S. 147, 153-54, 99 S.Ct. 970, 973-74, 59 L.Ed.2d 210 (1979). These interests are implicated when, as in this case, nonparties control the litigation in the first action, and then sue in their own right in the second. Litigating nonparties simply are not “strangers to the cause.” Id. at 154, 99 S.Ct. at 974. Although Sumitomo and Charter Oak were not technically “parties” to the state court action, they did control the litigation. The Supreme Court has stated that “one who prosecutes or defends a suit in the name of another to establish and protect his own right, or who assists in the prosecution or defense of an action in aid of some interest of his own ... is as much bound ... as he would be if he had been a party to the record.” Souffront v. Compagnie Des Sucreries, 217 U.S. 475, 487, 30 S.Ct. 608, 612, 54 L.Ed. 846 (1910).
Because this is a diversity case, the district court correctly looked to Pennsylvania law in applying finality of judgment principles. The court did not, however, identify the correct theory of preclusion. Under Pennsylvania law, Charter Oak is barred from bringing the action for indemnity by virtue of res judicata, not collateral estoppel. The Supreme Court of Pennsylvania, in Williams v. Lumbermen’s Ins. Co. of Philadelphia, 332 Pa. 1, 5-6, 1 A.2d 658, 660-61 (1938), held that one who controls or substantially participates in the presentation on behalf of a party is bound by the judgment in that action and is barred from bringing another action upon the same claim. See also Estate of Flinn, 479 Pa. 312, 322, 388 A.2d 672, 677 (1978) (citing Lumbermen’s for proposition that “one not a party to litigation may be bound by it if he openly and actively, with notice to adverse party, assumes and manages the litigation.”).
Charter Oak controlled the litigation in the state court and asserted the same claim for indemnity in its cross-claim against Yamaha as it asserts here. In defining the “cause of action” for purposes of preclusion under res judicata, the fact that the state court cross-claim may, as characterized by Judge Weis, have asked for relief under a common law theory of indemnity and duty to defend, while the suit in federal court sought relief based upon a contractual theory, is irrelevant. The conduct complained of is the same in both cases; failure to indemnify and pay costs of defense. The “plaintiff is not entitled to another day in court if he merely proposes a different theory of recovery based upon the same ‘liability creating conduct’ of the defendant which gave rise to the first action.” Ley v. Boron Oil Co., 454 F.Supp. 448, 450 (W.D.Pa.1978). Accord, Williamson v. Columbia Gas & Electric Corp., 186 F.2d 464, 470 (3d Cir. 1950), cert. denied, 341 U.S. 921, 71 S.Ct. 743, 95 L.Ed. 1355 (1951); Cemer v. Marathon Oil Co., 583 F.2d 830, 832 (6th Cir. 1978); Seamon v. Bell Telephone Co. of Pa., 576 F.Supp. 1458, 1460 (W.D.Pa.1988). See also IB J. Moore, Moore’s Federal Practice 110.410.1 (2nd ed. 1984).
At the commencement of the state court trial, Charter Oak had been in possession of the insurance policy and vendor’s en*271dorsement for at least two months. It cannot escape the effect of res judicata simply by failing to introduce any evidence based on the contractual theory. We agree with the district court in the Ley case which stated, “[i]n determining whether two cases involve the same cause of action, a basic concern is whether the plaintiff had a ‘reasonable opportunity’ to advance in his first day in court those claims or theories of recovery which he advances in his second.” Ley, 454 F.Supp. at 450. Here, Charter Oak certainly had the opportunity. Moreover, Charter Oak’s participation in the state court litigation clearly rose to the level of control necessary to apply preclusion rules. See, e.g., Ransburg Corp. v. Automatic Finishing Systems, Inc., 412 F.Supp. 1357, 1363-64 (E.D.Pa.1976) (where “the non-party actively and avowedly conducts the defense, manages and directs the progress of the trial at its expense and under its supervision, the outcome, which if favorable would have redounded to his benefit, if adverse becomes sauce for the goose and gander alike, and binding under principles of res judicata.”). Application of the Lumbermen’s principle here results in an absolute bar to Charter Oak bringing the action for indemnity in federal court.
Both parties to this appeal, as well as the district court, addressed the application of collateral estoppel to specific issues litigated in the state court action. Perhaps they were misled by federal common law in this area. The Supreme Court of the United States, in Montana v. United States, 440 U.S. 147, 154, 99 S.Ct. 970, 974, 59 L.Ed.2d 210 (1979), stated that preclusion of non-parties who control litigation “falls under the rubric of collateral estoppel rather than res judicata because the latter doctrine presupposes identity between causes of action. And the cause of action which a nonparty has vicariously asserted differs by definition from that which he subsequently seeks to litigate in his own right.” Accord Restatement (Second) of Judgments § 39 (1980). But while the courts label what they are doing collateral estoppel, they frame the “issue” which is to be precluded so broadly as to make issue preclusion in this context virtually indistinguishable from res judicata.2 Thus, the result under federal common law is in effect the same result as under Pennsylvania’s more straightforward application of res judicata. We approve the Pennsylvania approach and believe that the principles behind claim preclusion justify its application in this case, where the insurance company litigated the case in the state court and now seeks another chance in federal court.
Charter Oak also claims that Sumitomo wrongfully failed to defend it in the state court action. We find the failure to defend claim barred by res judicata under the same reasoning as we set out above. In the state court action, Wodarski asked for “costs of defense.” Whether the theory relied on was contractual and based on the insurance policy and vendor’s endorsement, or based on principles of common law indemnity, is irrelevant. Plaintiffs in this action should not be given another chance to litigate issues “which they have already litigated or had a reasonable opportunity to litigate.” Williamson v. Columbia Gas & Electric Corp., 186 F.2d 464, *272469 (3d Cir.1950). Here, as in the Williamson case, the “only thing that is different is the theory of recovery.” Id. at 470. Charter Oak’s claim for damages for breach of duty to defend, therefore, is the same claim, for purposes of res judicata, as Wodarski made in the state court action under the name of “defense costs.”
But even if res judicata did not bar it, we would affirm the district court’s dismissal of the duty-to-defend claim on the ground that Sumitomo had no duty to defend. The insurance policy in this case contains two clauses which, when read together, impose a “duty to defend” in “any suit against the Insured seeking damages on account of such bodily injury or property damage, even if any of the allegations are groundless, false or fraudulent.” App. at 43. Wodarski became an “insured” by virtue of the vendor’s endorsement, app. at 47, but only to the limited extent of the endorsement. Appellant argues that Sumitomo had a duty to defend Wodarski regardless of the merits of Peterson’s claim against Wodarski or the facts potentially excluding the claim from coverage. It is true that, according to the Supreme Court of Pennsylvania, the “obligation to defend arises whenever the complaint filed by the injured party may potentially come within the coverage of the policy.” Gedeon v. State Farm Mutual Automobile Ins. Co., 410 Pa. 55, 58, 188 A.2d 320, 321 (1963); Brugnoli v. United National Ins. Co., 284 Pa.Super. 511, 516, 426 A.2d 164, 166 (1981). But it is also true that under Pennsylvania law the insurer need only defend “until it can confine the claim to a recovery excluded from the scope of the policy.” Seaboard Industries, Inc. v. Monaco, 258 Pa.Super. 170, 176, 392 A.2d 738, 743 (1978); Brugnoli v. United Nat. Ins. Co., 284 Pa.Super. 511, 516, 426 A.2d 164, 166 (1981). See also Pittsburgh Plate Glass Co. v. Fidelity and Cas. Co. of N.Y., 281 F.2d 538, 540 (3d Cir.1960).
In this case, Wodarski did not demand defense from Sumitomo until March 26, 1980, almost three years after the state suit commenced. App. at 416. By that time Peterson had filed its pre-trial narrative statement which clarified the issues for trial to the point where it was clear that the claim to be tried fell outside the coverage of the insurance policy. In the pre-trial narrative Peterson stated that the “throttle mechanism [of the snowmobile] had been improperly assembled by the defendant Wodarski and it was the improper assembly which caused the throttle mechanism to stick.” App. at 21. Since the vendor’s endorsement excluded coverage when there was an intentional change in the physical form of the snowmobile by the vendor, Sumitomo properly concluded that the claim was not covered and it had no duty to defend. Indeed, less than two months after Wodarski’s demand for defense, the trial court dismissed the claim against Yamaha by Peterson and the cross-claim by Wodarski for indemnity and costs of defense.
Under principles of finality and fairness the district court acted properly in precluding Charter Oak from litigating this case. The judgment of the district court will be affirmed.