This problem has agitated me for a while now. I called Ford to see how much to replace them, ($$$)! I pulled out the panels today to see what I could do with them, and found the problem. The roller has only one bolt holding it on and after years of use, the roller twists and this causes the belt to track off to one side and hang up. To solve the problem just twist the roller assembly to where the belt tracks evenly. Problem solved!!