Change the starter drive. There's a one-way clutch in it that appears to be slipping intermittently instead of turning the flywheel. It's a pretty common failure of a worn-out starter drive. (sometimes called a "Bendix", which it isn't)
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!