Try a rotation and balance...that way you can relatively eliminate wheels/tires as the culprit (and ask that they check for a bent rim) and might fix the problem.

If this cheap way out gets you nowhere, and the techs agree that it's a drivetrain thing, then you need to determine if that shop has a driveline/drivetrain alignment tool. Perhaps one of the experienced techs kind enough to participate in this board can elaborate further. Hope you get away cheap :cool !

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Best regards, Michael
'92 500E
'88 300TE