Here's the information I can find on the rear axle (differential).
I checked the Owner's Manual, Service Manual, and TSBs through 2006.

Service Manual:

Quote:
DESCRIPTION - DIFFERENTIAL LUBRICANT
Note: Refer to the Owner’s Manual for the recommended differential lubricant change intervals for this axle.

Rear Axle Fluid Only use synthetic SAE 75W-85 axle lubricant that meets MB 231.1.
Reduced axle durability may result if an unapproved product is used.

1. Drive the vehicle until the differential lubricant is at the normal operating temperature.
2. Raise and support the vehicle.
3. Remove the differential housing fill plug (1).
4. Position a drain pan under the differential housing drain.
5. Remove the differential housing drain plug (2).
6. Drain the differential housing completely.
7. Install the differential housing drain plug (2). Tighten the drain plug to 50 N·m (37 ft. lbs.).
8. Fill the rear axle to proper specifications.
9. Install the differential housing fill plug (1). Tighten the fill plug to 50 N·m (37 ft. lbs.).