Try not to drop them?
I was thinking about how to repair these terminals, but I fear that it would be considered a modification and make the motor illegal for competition. However, for practice, my idea was to drill a very small pilot hole next to the broken terminal in its plastic berth. Into this would go a small screw whose threads would contact the remaining metal of the tab. Electrical connection to the screw might be done by ring connector if it were on top of an insulating washer. That is, screw goes thru ring connector, insulating washer (fiber or plastic) then into pilot hole in plastic. I haven't done this yet, haven't needed to. This is only a plan, so if you try it let us know how it works. Good luck!