I agree with Joe, usually a good cleanup will take care of one of these motors (and wiring if necessary of course).
Depending on the symptoms - try to fire it up as long as the wiring doesn't look damaged - and tell us what it's doing or not doing - it could be as simple as the brushes are worn out and need to be replaced. That's less than a $10 fix, even with shipping and something you can do yourself. The carbon part of the brushes should be longer than 1/4" ( how to check the brushes will be in the service manual Caroline S linked to) I do like to do the full "Service" on the motors, like what Joe does, I just figure if I'm in there, I might as well do it all so I don't have to go back in again any time soon.