Ok my hubby is helping me rebuild my rally car and I want to shim the diffs and refill them with some diff fluid but I am unsure s to wht weight I should use in the fron and rear. Any help would be apreciated. I mostly use the car for speed runs and sometime attempt a little drifting. Should I also refill the center one or is it not refillable? Thanks for any help. Wnna suprise the hubby and go to the hobby shop and have all the stuff there when he gets home.