I have searched the SLK230 forums & cannot find anyone else with this problem. When I lower the roof... the back edge of the top actually hits the top of the rear bumper, binds a little, then slides over it & continues to lower... this is scratching my rear bumper top. If someone else inside the car lowers the roof I can push in on the rear bumper (it will push in about 1/2") & the top continues without a problem. What caused the bumper to "expand" in the center. I can't seem to find a center bolt that would tighten up the bumper center (is there a center bolt?) 1999 SLK230 with 50K miles