Starter

I replaced flywheel and starter six months ago. Recently, the engine was slow to turn over and I thought it was the battery. Mechanic checked and said it was starter and rebuilt it. It cranked fine for a few days but now, once or twice a day the first time I turn key it sounds as if starter just spins but then it always cranks the next time I turn key. Any ideas.

Take itback to the mechanic, it sounds like the starter drive ( some call it the bendix) isn't engaging all of the time, hence the whirring noise. If the Mech "rebuilt" it he might cover this, or perhaps you could get a new or rebuilt starter from your local parts store and stick it in yourself.

Either the solenoid isn't pushing the drive out to engage the flywheel, or the drive itself is shot. Sometimes they wont grab on the first try, then the spin seems to loosen them up and the next time it will grab, but it wont get any better by itself and might get to the point where it will leave you stranded.