I have a 07 650i. What fluid goes in the rear axle and what fluid goes in the front. My buddies are using synthetic 80w(typical truck diff fluid) in both. Not sure that is right
I would use the Kawasaki specification for the front axle, which calls for API SF or SG, or API SH or SJ with JASO MA Class
— Viscosity SAE 10W-40
— Capacity 0.4 L (13.5 fl. oz.)
The reason you do not use 80w90 or other regular gear grease is that it will glaze and crack the front differential clutches, cause them to start disintegrating and chew up the bearings in the front differential.