Slipping treadmill: Proform 745CS?

Okay, my problem is a slipping tread belt. I think that's what it's called; the mat that you run on. Anyway, it's slipping. Now, this should be easy to fix. As detailed in the manual, I need to use an Allen Wrench and turn two screws, one on either side of the tread belt on the back of the treadmill, clockwise until the tread no longer slips. This is also the method of returning the belt to center, though the screws need to be turned different directions for this.

Now, all of that seemed straight forward, but reality rarely is so easy. I turned the screws to center the tread band, and then tightened it down to prevent slipping. Before I was able to fully get it tightened, the tread had already migrated off center again. Any time I tested the band for slippage, it moved to the right immediately. Upon closer observation, I noticed that the rear roller has worn into the plastic retainer on the right (which is where the belt migrates to).

So I have two problems, the belt won't stay centered, and it slips. I imagine both are related to the problem of the roller eating into the plastic retainer, but I have no idea how to fix the problem. Any ideas? I can provide pictures as well as the manual in PDF format if it would help.

Thanks for any help guys, I'd really like to take care of this problem.