I recently reworked my seat rails. Are the shims you mention thick black oval-shaped washers? I only found them under the passenger seat, which was a b***h to get out as it didn't want to move at all. To avoid any chance of the rails bending, I cut lengths of 1/4' thick steel and installed them between the rails and the floor, and between the rails and the holes in the seat. I may have lost a bit of headroom but figure the carpet will compress further in the coming months. I also put in new wheels cut from Delrin plastic, per the advice of this great forum. The seats glide now!