5-7-3 or 5-7-2 will work great. You have to change the fluid in hour diffs and in your shocks after every gallon of fuel or usually 4-5 race days depending on how much practice you do. The fluids get hot and wear out then they lose their consistency and these buggys are touchy. As for cleaning them I take them apart and spray them down with electrick motor cleaner, let the gears soak in some motor cleaner, dry them off and reassemble them. Fill the diff up so it just covers the gears. You don't want to over fill them. Proper maintence is critical.