I had a bit of a problem at the dealership today, trying to get the correct differential fluid for an '05 ML500. The fluid should meet the MB Sheet 235.7 specification, and be of an 75/80W-90 viscosity. But the fluid they sell as "OEM" (Fuchs Titan Super Gear MC 80W-90) did not. It meets both API GL-4 and GL-5 (which I found rather interesting, since these seem not to be interchangeable in some applications), and various other manufacturer specifications like Scania and MAN's own spec. At $14 per litre, I told them to keep it. Does anybody know if Mobil happens to carry a differential fluid meeting the MB Sheet 235.7 specification? My search hasn't lead me to find anything. Would it be alright to substitute something like Motorcraft Premium Rear Axle Lubricant 80W-90, and change it out at 40,000 km (25,000 miles) as opposed to the recommended 100,000 km (60,000 miles)? Thank you.