maybe someone mentioned this before but here goes.. have you checked the clearance between the starter teeth and the flywheel teeth ?..take a set of needle Nose pliers and pull out the starter gear and see how far in its meshing with Ring gear. If your getting in too deep there could be a bind not letting the starter gear retract properly causing the damage you mentioned..if your starter has the least little movment after running for a while it could cause the mis-alignment also