I've been running the Spec-R gear diff in the rear of my 416 in MOD TC with a 4.5 motor. So far it seems to work fairly well for 2 weekends of racing. I have not had any major issues with leaking oil from the pulley, however I do notice that oil is coming out of the outdrives. I am using green slime on the case gasket. Should I be using something on the outdrive o-rings to seal it better? Right now I am using AE black grease on them.
Also on a sidenote, I installed the Spec-R CV2 dcj's and they have held up to 2 weekends of MOD. They have quickly developed slop, but they are still working. How often should I be rebuilding/replacing parts on the units?