Position Control Dial on T700

[dcgrosvold]

Anyone else have a T700? I have a Montana-badged T700 that has a "position control dial" (their words) that controls the raising and lowering of the 3-point hitch. I have had trouble with it from day one. When I try to run it, it slips past the stops and keeps going in either direction. I've removed the cap and tightened the lock nut on the shaft, but no matter how tight I try to make it, one or two turns and it goes right back to slipping. It appears to be one of the cheap lock nuts with a nylon center.

Anyone else have this problem? If so, is it as simple as putting a better lock nut on it?

Thanks!