CarbDoc

I have a Shop Fox W1676 6/10 belt sander, 5+/- years old which I use daily to resurface aluminum, pot metal and cast iron castings. I replaced the platen due to 'cupping" and the cam, cam plate and cam plate busing about a year ago due to the belt overrunning the lever side of the platen. It is now overrunning again and I don't know why; all of the replaced parts have been inspected and are still in good condition. At the extreme of the roller adjustment travel, the lever side of the roller is about 1/8" to 3/16" short of the opposite (belt drive) side, so it is understandable as to why the belt runs off to the laver side. Is anyone familiar with these machines? i sure hope so, because I am stumped. Jeff