Hi friends. Greetings from Malta.
Can't say I've had any problem with either centre shaft cups or diff gears with my SDs, even running 8 turn motors and spools.
The only time I blew a front diff gear was when I tried removing a couple of shims to reduce friction. However since I have been running stock shims I haven't had a problem.
I know people that have had problems with TC3 cups too, though again we have never had any such problems with my son's car that is now in it's 5th year of racing and winning.
An easy solution however is to slide a length of shrink tubing over it, possible double it too. I'm sure that should solve the problem. I do that with the outdrive part of the spools, both on the TC3 and the SD, but more to keep the blades located than for any other reason.
Regards
Joe from sunny Malta.