[James]

This is what I would do:
1. Removed the starter.
2. Clean the Bendix and shaft with Mineral Spirits. Then blow dry with compress air.
3. Lubricate the Bendix and shaft with silicon spray. Spray everything (Bendix and shaft) and let is soak into the Bendix. You can move the Bendix by hand to help the internal get lubricated. Let the excess run off. Do not wipe off.
4. Reinstall the starter and the problem should be gone.

Note: They make two different kind of silicon sprays. One type is running, this is what you need. The other is very thick and will not run off, do not use.

This was taught to me 60 years ago. Hope this is helpful.