1) Check the battery, it may be bad even though it doesn't seem bad....
I'll buy that, I've got a jumper/starter/battery charger that I can run
directly to the starter leads.

2) The rebuilt starter has a bad bendix. Bendix has been recalling parts
lately, it could have some bad ones in it.

3) One fellow on another forum had a bad battery cable causing the problem

4) Another fellow on another forum didn't have the correct washers and nuts
on the starter stud, causeing arching.

5) Misalligned starter gear w/ring gear causeing binding and old starter
shaft problems as well as new starter shaft problems.... OK. the starter
mount has 2 alignment studs and 4 bolts, everything lined up good there and
it tightend up flush to the engine. So does that mean that the ring gear
might be misalligned? That's starting to sound spooky.