Originally Posted by bobs

According to the manual, the differential is filled for life. General consensus on some of the M-B specific forums I read is that the stuff really needs to be changed after 30k-50k miles.

One tip for doing the fluid: Remove the fill plug first! That way you're positive you can get it out before you pull the drain plug. Someone on another forum removed the drain plug first and then stripped-out the fill plug trying to get it out. He had no way to get oil back into the diff and had to have it towed to the shop.

Another tip: Make sure you clean the plugs thoroughly before you try to get them out as dirt & grime will get caked up inside them. You want maximum wrench-plug contact. If I remember correctly, it takes a 14mm allen wrench with an 18-24 inch pipe extension to break the torque on the plug.