The problem that's being described (read the original post) is a very common one to anyone with experience with rebuilding GM starters. The one way roller clutch in the drive develops flat spots on the hardened steel rollers that allow the shaft to spin in both directions. Eventually after several attempts at starting, one or more of the rollers turns enough to let the gear engage and turn the flywheel.

Just replace the starter drive and quit over-thinking this one. It's an easy fix.
Jerry

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