has not drawn a “rigid distinction between negligence and strict liability failure to warn concepts.” Romero v. International Harvester Co., 979 F.2d 1444, 1452 (10th Cir.1992). For example, as with all tort claims, the plaintiff must prove the elements of causation and damages. More importantly, “[o]ne critical area of overlap is that, ‘[rjegardless of whether a product liability action is grounded in negligence or strict liability, a plaintiff must prove that the product was defective.’” Perlmutter v. United States Gypsum Co., 54 F.3d 659, 663 (10th Cir.1995) (quoting Mile Hi Concrete, Inc. v. Matz, 842 P.2d 198, 205 (Colo.1992)). Under either theory, the product must have been defective at the time of sale. See Perlmutter v. United States Gypsum Co., 4 F.3d 864, 869 (10th Cir.1993) (<HOLDING>); Fibreboard Corp., 845 P.2d at 1175 (stating
holding that the defendant trade association which did not manufacture sell distribute design test conduct safety research on or set standards for the product could not be held to have owed a duty to the plaintiff holding a successor corporation does not have a postsale duty to warn of product defects where the successor never succeeded to any service contracts was not aware of the products defects and did not know the location of the product at the time of plaintiffs injury holding that in a negligence claim there is no postsale duty to warn or remedy when the product was nondefective under standards existing at the time of manufacture holding a manufacturer had no postsale duty to warn of dangers associated with an auger because numerous hodder factors were not present holding there is no duty to warn of risks obvious to the average user of the product