There's some good information in here on this job. If you want my particular experience then search on "starter" as the subject and "Ken300D" as the member name.

The easiest removal to me seems to be the following:

Front of car up on ramps. Jackstands will kill you.

10mm allen socket, 3/8" drive. Universal joint, 3/8" drive. Socket driver extensions, 18-24" total. 3/8" driver, or better, 1/2" with 3/8" adapter.

Snake the extensions with universal joint and allen socket on the end up by the transmission, about half the way back along the passenger's side of the transmission pan. Fully seat the allen sockets into the bolt heads. Clean bolt heads of gunk if necessary.

To drop the starter I found the steering dampener (shock absorber) needed to be undone at the passenger side end.

I did this job twice. First was a used starter from EBay. Within two months it exhibited the exact same problem, spin but no catch on flywheel.

I can recommend the Bosch rebuilds sold here on FastLane. Not extremely expensive and well rebuilt.

This is not a bad DIY job with the right tools and tips.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles