shoulda posted this in the cyclone thread! The diff's on these cars are awsome, they last a long time in between rebuilds. I don't know what diff balls your using, I will assume steel. I like to just do a simple clean and re-lube, I hardly ever replace parts inside my diffs anymore. I think replacing parts that aren't broken is a waste of $$. Unless theres deep groove, scores, or bends in the diff rings or thrust washers. The balls almost always outlast the diff rings/thrust washers. Especially if your using silicone Nitride ceramic diff balls.
My cyclone diffs will get gritty after about 30-40 runs which is incredible. Simply take your diff's apart, clean all the junk and dirt out of them, packem with diff lube and diff grease, tightem them up full compressed, then back out 1/2-3/4 turn.
Check them after your first run!