RE: Centre diff oil fill or not?
It sound like you have a RTR. check to see haw many spider gears you have in there, I upgrade to 4 in each diff in my truggy, thoroughly cleaned them out and replaced with silicone oil, and wow, what a difference, also keep your eyes on the shimming, to make sure everything is smooth. This is one of the best improvements you can make to your ride, good luck with it