ok, i got some new diff oil since mine are a bit gritty. i have some 3000wt and 5000wt. some people told me i should have bought some heavier stuff, like 30k and 50k or so. anyways, i want to know, what part of the diff do i fill? just the cup? the case? do i fill it up completely or just stick it on the gears? any how to pages would be helpful too i also bought some shims to help gear mesh...