You may have already done this, but before you pull the starter off that's giving you trouble, climb under the car and see exactly what the problem is. Check the engagement, check to see if the starter has moved/shifted since it was first installed. Another thing are you useing starter bolts with the knurled body, or are you useing regular 3/8" bolts. If you are useing regular 3/8' bolts the starter will definately shift after a few starts. Starter bolts (knurled) have a .390 body dia. VS a .375 dia. on a 3/8" bolt.
Just looking :idea:
Zip.