In Eljer Manufacturing, Inc. v. Liberty Mutual Insurance Co., 972 F.2d 805 (7th Cir.1992), cert. denied, 507 U.S. 1005, 113 S. Ct. 1646, 123 L. Ed. 2d 267 (1993), the product involved was a plumbing system which was manufactured and sold to plumbing contractors nationwide. Within a year after the first units were sold and installed, complaints were made regarding leaks and several hundred products-liability lawsuits were filed, some of them class actions. It was estimated that ultimately five percent of the total number of systems sold would fail in circumstances likely to result in a lawsuit. Speaking for the majority, Judge Posner concluded that for purpose of determining coverage, "physical injury to tangible property" occurred when the allegedly defective plumbing system was incorporated into a larger structure, such as a house or apartment, rather than when the system actually malfunctioned, causing physical damage to the structure. Eljer, supra, 972 F.2d at 814. However, in order to constitute the physical injury as of the date of installation, the expected failure rate must be sufficiently high to mark the product as defective and induce a rational owner to replace it before it fails. Id. at 812.