I also use 80-90 Synthetic in the final drive, and Mobil one in the engine and Trans., most automotive stores have it. It seems quiter and works less.
Just remeber, when you fill it (on the centerstand and a level surface), turn the wheel by hand a few times, and check the level again. You will need to add a bit more. It won't over fill because the oil level hole will drain off the excess.
I do the same for the engine and trans. I run it a bit (then wait about 2-3 min. after to allow for the fluids to settle) and find the level changes.