In some cases it depends on the year and model. Some folks use OE fluids and some use aftermarket choices. I suggest going to a website such as ECS tuning, FCP euro, Bavauto etc. where you can enter the year and model of your X5 and it will pull up the correct fluids. Other than engine oil, since the design of diffs, transmissions, transfer cases included the fluid. I use OE or OEM fluids.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas