yeah they are just different viscosity ratings. i have found the best way to clean the diff is to use degreaser (the one that doesnt leave any residue behind), spray the gears and just basically clean the whole diff up with it and then put your gears back in and fill the diff upto the top of the satellite gear (about 80% full) and put it all back together.

you should also change your o-rings in side the diffs and maybe your bearings if they are bad.
hope this helps.