Back in my day.. I had a car that ate those bendix gears like they were M&M's I kid you not more than a few months was .. Rare.. (I finally replaced the flywheel ring gear)
I got so I kept a spare gear. Since it slipped nicely over the gear shift lever (FLoor shifter) I simply unscrewed the knob, slipped a spare on and replaced the knob, that way I always knew where the spare was. 15 minutes on teh side of the road or in a parking lot and I was good to go.
If it is the gear.. Find a Starter/Alternator shop. they can still get 'em way cheaper than a new starter.. Walters in Redford, MI is where I got mine, On Grand River.