just sharing... "repairing" notched diff outdrives (gear, ball):
1. add a blob of epoxy over the notches
2. let it harden overnight.
3. sand/dremel the blob flat so only the notch is filled.
4. sand the slots with 1200 or finer sandpaper to smoothen it
5. (i also take the "edge" out of the slots with a dremel"
pic attached is an outdrive for a mini but i've done the same to my SpecR and Tamiya white gear diff.