oleblue51,
Hopefully, when the starter was rebuilt they installed a new starter drive. The ring gear is pretty tough so it can be chewed up, but usually not enough to cause the drive to actually spin through the teeth.
My thought would be to check the linkage for worn joints. If the mechanism is worn to the point that it closes the starter switch BEFORE the starter drive is fully engaged, it could result in gnashing and grinding...especially if the ring gear were worn.
I think you can fiddle with the starter switch and fine tune it to be back as far as possible, which would allow the mechanicals to be better meshed before the starter actually started spinning.
Stuart
