My starter would freewheel every now and then on my 4-cyl, so I pulled the starter to replace it. This is what I found:
The previous owner left a surprise for me in the form of two broken studs, still in the bell housing.
Which means there was only one bolt actually holding the starter in place.
Which means it'll flex under torque and take out some ring gear teeth.
Toll: One broken tooth, a dozen more severely worn, and the rest don't look so hot either.
I did manage to remove the broken bolts (after LOTS of PB blaster over three days, vise-grips, lots of heat, nothing worked). So the plan became, drill them out, run a tap through to clean up the threads and reassemble.
The bottom bolt, I was able to drill from behind. Since that was the case, I didn't need a left hand bit to back it out. Got a little way in and I was able to turn the stud out with the vise-grips. That took about 10 minutes.
Incidentally, it's a 21/64 bit for the final hole, if you're ever wondering.
There wasn't enough clearance to hit the top bolt from the back so I had to do it from the front, and that took a LOT of time - progressed through 1/8, 1/4, 5/16, all left handed bits. Finally managed to get through it. Still couldn't back out the remaining fragments, my guess is galvanic corrosion had it in there TIGHT. This, I found out when I tapped the holes. First two, really easy. Top one: No way, bits of bolt had anchored themselves into the threads for eternity.
So, plan C for the top bolt: 3/8 drill straight through, mount the starter with a long 10x1.5 stud and backing nut. Finally, victory, though diminished.
Final score: two bolts restored to factory spec, one with an alternative that isn't ideal to me but it will hold solid. Far better than what I found, at any rate. Someday I'll helicoil it so it's done right.
Bottom line is the starter itself is fine, so the old one is back in. The flywheel is the problem at this point, so I'll obviously need to plan replacing it sometime (along with a clutch job whenever it comes along). I have no plans to pull that thing apart right now. For the time being, if/when that bad spot lines up with the starter, I'll just need to bump start it. I can live with that for a little while - just kinda bites that I need to.