Diesel Bombers - Starter with broken gears. Questions on cause and repair (98 Dodge 24V Cummins)

The Issue
My 1998 Dodge Ram 2500 24V Cummins would not start. The first three times, it would turn over but would not start. It was audibly normal so I assumed it was unlikely due to a low battery. I thought that it was fuel related.

Unfortunately and after waiting 20 minutes, I attempted to crank and heard a screeching sound similar to a belt slipping. Then the starter spun freely and the engine did not turn.

I pulled the batteries. They were a bit low but could have been from not driving for a while or the four attempts to crank. I charged them overnight.

I pulled the starter. The flywheel teeth looked good; however, I did not turn the engine to see above or below.

The plunger and the contacts were marked; however, they are still relatively smooth and appeared in good shape. In the photos below, you can see the marking. Both the plunger ring and the contacts inside the solenoid are smooth to the touch. Any time I have seen this as an issue is if they look chewed up significantly.

I pulled the starter motor off of the starter and noticed that the spindle's teeth looked slightly worn. Closer inspection of the gears inside the starter case showed three missing teeth.

The question
1. What is likely to have caused this. I want to make sure I do not screw up the replacement. The rubber on the cable from the solenoid to the starter motor was almost non existent and it could have been shorting itself out. I will have to look at the wiring diagram but could a short like this engage the starter motor prematurely causing the issue?

2. I have seen rebuild kits for the plunger and contacts. Has anyone successfully replaced components within the starter gear box? The case is sealed with three philips head bolts. Unlike all of the other hardware on the starter, these three bolts are on tight. Any additional effort and I would have stripped them. I could add heat or drill them out.

3. I have read some pretty bad reviews on aftermarket starters. Any suggestions or recommendations?

http://sligh.us/storage/plunger.JPG
http://sligh.us/storage/solenoid.JPG
http://sligh.us/storage/starter.JPG