normally its said you don't need to change the diff oil as it isolated from engine combustion. usually 90ep BUT don't tae my word for it go to car spares shop they will look up grade for your type of vehicle.
On you're own head if you chose to use 90 ep without checking. I think the reason you have to change engine oil is the contamination of combustion products weaken/effect its purpose.
bob UK, July 2014
