52" Wright Velke walk behind. As the picture shows, I made two passes together. What the heck could be causing the dark stripe that you see? I know that it is the left most 3 inches or so of the deck. It happens even when the deck is cleaned spotless. Can't be a belt problem. Spindle?? The left one seems ok. The deck belt is riding a little high on the IDLER pully, but that shouldn't be it. Any ideas????