Try cranking the engine with a 12V battery, or just use jumper cables from a 12V vrhicle for a short burst to see how the starter reacts. It's not a fix, just a troubleshooting tool. If the engine cranks noticeably faster, PM me for some guidance on doing a "series resistance test". It's a bit too complex to describe on the open forum with a dozen others arguing about how, or if the test should be done.
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!