Well after explaining to my class in GREAT detail all of the components within a starter, what they do, how they work, how to test every single component and overhaul them I am left with 2 good starters

Not that it's that hard to do but why bother?
Anyway if your starter is engaging and not disengaging and it is overrunning then the starter solenoid is sticking and that's your problem. That's an ez repair. If the motor is turning your brush repair kit is a waste of $$