I cant seem to figure out which diff fluid to use for my 06 E55. I've searched through threads where owners have used 75w-90 synthetic but when I call some local dealers they all say something different. One says 75w-85, one says 75w-90, and one says 75w-140. I can't seem to find a definitive answer anywhere. Also some sources say it needs some sort of "hypoid" type of oil but not sure what that means or if that's even true. If anyone can chime in & let me know which fluid works for you that would be great, thanks.