Cannon assemblies are troublesome in ST TNG. I've not heard of this particular issue, 90% of the problems are in the wiring looms that feed through to the sensors, plunger etc. I'd be checking the "home" switch in the switch diagnostics and then check the lugs on the motor to see if they have a good solder connection. The gears should have no lubrication on them as it will bind the mechanism and cause friction.
