The problem thats lasted two years!!!

[Unit 5302]

There are a limited number of possibilities.

Starter
Flywheel
Bell Housing
Block

The block is very unlikely to be the problem as the bell housing will not line up to a block with a crack large enough to cause your problem.

The starter you've replaced. Did you bench test it to make sure it was engaging fully? I've gotten several bad "rebuilt" starters over the years.

The flywheel you had re-ringed, but you didn't actually replace it. The engine usually stops at one spot. If the flywheel was damaged or warped, it might be out of round causing the issue? I also believe this is entirely unlikely as the engine would be out of balance pretty bad with such a problem.

Finally, the bell housing itself. You were able to "screw the starter in sideways?" To the best of my knowlege, there are three starter bolts, and the starter slips into the bell housing quite snugly when it's mounted properly. Did you inspect the bell housing for any cracks or damage that might be offsetting the starter? I've seen damaged bell housings before.

If the bell housing is okay, and the block is okay then it really leaves only two parts that could be causing the issue.