Is it possible to fit diffs other than the Mugen diff in the RCM hybrids? I really prefer Losi diffs, just curious if they're usable. Figure since we're on the topic of the hybrid diffs and the question has been answered, this is one worth asking.

I have additional question about V3 diff.
The plastic inner case is made for 6mm output shafts.
I know Mugen diff case has 5mm bore for output shaft. I believe Caster inner diff case has 5mm bore, too. Any direct replacement of the inner case for 6mm shaft?

I think Xray diff might be the cure.

Revo Hybrid Diff Assembly Instructions
 

Looking at the pic of the different parts of the Hybrid Diffs, it really looks like the input shaft is 8 mm with the tip machined to accept the Revo shaft. Im sorry I cant be 100 sure but it really looks like you need a 12X8 bearing like magman said.