RE: Rebuilt Starters (and alternators)
I've posted this info before and I'll post it again.  Quite some years ago
(but still valid) I had a face to face conversation with a guy that did
starter/alternator/generator rebuilds, he was the supplier for a friend that
owned/ran an auto parts store.  Bottom line:  80% or better of the 'bad'
units only needed cleaning and new brushes, some needed the commutators
turned and some needed bearings, most fixes a shade tree mechanic can do.
But by far the biggest problem was just worn brushes.  Actual burned out
units were rare.