Hello. The propulsion mechanism on my 1989 LM21S slips and begins to smoke when either the drive speed is too high (the drive speed regulator lever moves on its own accord) or the mower is going up hill. I have found replacement parts online (Drive Plate (01127300) and Friction Wheel (51109700)) but, since they're around $50 each, I'm wondering if I need to replace them both or if one is typically the culprit for the conditions that I'm experiencing and therefore the only one I would need to replace.
