I called Autozone and all they have in Mobil 1 differential fluid is 75W140. http://www.mobil.com/USA-English/MotorOil/Other_Products/Mobil_1_Fully_Synthetic_Gear_Lube_75W-140LS.aspx

I don't have a specification manual anymore, but I thought it was supposed to be closer to 90 weight oil. Is 75W140 too heavy for a differential?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles