Have you tried replacing the horizontal damper in between steering ends? I don't know if it will solve the underlying problem, but it may make it less noticeable, and they only cost about $65. Have you cleaned the antiskid sensors on the front brakes? Metal deposits on the sensors caused a pulsation at very low speeds for me.

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