Tony
If you have a w124 and this may apply to other MB's with age or exposure the lower front ball joints can seize and cause this same shimmy. I had one and went through several wheel balancing experiences and an alignment, until I read up on this, changed the ball joints, and she rides beautifully.

Cheers

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)