Starter grinding

Motors tend to stop turning at the same spots when shut off (like 4 of them around the flywheel)
This wears on those same four spots every time you start the car, and the "go to" for the problem was to replace the flywheel and possibly the starter depending on the starter gear condition.
If it only happens hot I would tend to thinks it's a problem within the starter and not the flywheel.
Something about the heat isn't letting the starter engage correctly, and if it was only a heat problem that a shield would fix then all of us without a shield would be having the same problem.

For about 15-20 bucks you could pull a used one off a wrecking yard truck and see if that fixes it.
Bet it does.:D