Jasper, You've got a good one then. I had to fight tooth and nail to get them to take the dead one back last time around.... they have a system now where the tester is hooked into the computer system and it woln't let the salesman warranty a starter or alternator unless it's got a 'failed' test on record from the test bench..... Since this one would test fine it's be an uphill battle from the start, not to mention trying to explain what its not doing...... not worth it!
Franklin, wear on the ring gear or starter can cause the issue and is most commonly the cause. In my case since it was fine till I replaced the starter and I know darn well the ring gear is fine I can pretty safely conclude it's the starter. The shim goes between the solenoid and the starter gear case. The solenoid has 2 functions - it pulls the lever to engage the pinion and then it closes the contacts to supply power. The lever is connected to the nose of the center section, and the contact is on a spring inside the rear case of the solenoid. If the solenoid is too close to the gear case or something else is out of whack, the contacts will engage before the pinion has traveled far enough causing the grinding. If you move the solenoid slightly further back from the gear case it will cause the lever to travel further before the contacts engage. Or at least, that's the theory..... Never actually messed with it, but I recall seeing some info on adjusting the position for this very reason with a replacement solenoid I bought at one point....