If you do try to repair your stock diffs, make sure they are shimmed. I have the older Emaxx and they didn't shim those diffs, kinda doubt they are shimming the new ones either - takes too much time.

If the pinion is spaced too far away from the ring, no amount of strength is going to prevent them from getting stripped. With you loosing ring gear teeth, sure sounds like a shim prob (lack of)??