Rear Bumper paint and bumper cap [Expired Topic]

My 2004 Suburban with a Z71 Package has been in twice to have the rear bumper painted twice. The bumper cap has movement in it and scratches the paint which in turn strarts to rust. The vehicle is under warranty and GM has said there is no for sure fix for this issue. They tell me it is a design problem on the 2004 and they are going to discuntinue to fix the problem. Has anyone esle had this issue? The first time the dealer fixed it I was told this was a known problem, the second time it was fixed I was told they have never heard of the problem and now that it is in need of the third fix they are denying any resposiblity. Any help would be appreciated.