Good advice from both of you. I will remove the fill plug first and I will try to do it without jacking up the car. It's been so long since I did my 400E diff. oil that I can't remember if I jacked it up or not. All I know is that I have a 17 mm hex wrench and a 17 mm hex socket that I had to buy to use on the plugs.

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