Yeah I have an 8ight-T, build thread is on here (MT section) too.

With a little bit of luck and/or ingenuity, you might be able to run the Losi or Durango cups in your cars. Otherwise, doesn't innovativeRC make some alu diff cups for RC8 or TT? I think I saw timritchieblue running those on his RC8T in a thread here somewhere. Technically, the steel inserts should be better, but alu cups might already solve your problem?