A shop may have put transfer case fluid in the front differential of a friend's 2007 X3. The above referenced transfer case fluid, Shell TF0870, is said to be SAE 75W Full Synthetic GL-4, and it has a sulfur smell like differential fluid.
My hope is no damage has occurred in the 4,000 miles they have driven it. Best I can tell, what goes in the front dif is 75W-90. That would mean it is a little light, but it was lightly driven mostly in winter.
What do you think?