Thanks to the many posts on differential fluid changes, I managed to change the differential fluid on my 98 E320.

I first remove the fill plug, then the drain plug (located on opposite sides). While the old fluid was draining, I remove the vent tube with my 17mm open end wrench. I removed the top cap of the vent tube and cleaned the felt filter and drain tube. After replacing the vent tube I put the drain plug back on and put in fresh differential fluid.

I noticed that the old differential fluid was dark brown in color (similar to pancake syrup) and only drained out 1.1 qts. The refill took 1.4 qts. which correlates to the manual.

Some helpful hints I used were to raise the car up on all four wheels and remove the driver side rear wheel. Place a 18" clear hose on the quart of differential fluid and position the quart jug up in the wheel wheel (this allows easier filling since the quart jug is at a higher elevation than the fill opening). Place the other end of the hose in the fill opening and commence filling until the fluid runs out of the fill opening (keep the drain pan in place to allow fluid to spill into the drain pan). Use anti-sieze compond on the threads of the fill and drain plugs to allow easier removing in the future. Wipe the differential housing with rags, this will alert you if there are any leaks.

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Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles