Carl,
If your car has > 100 k miles and the subframe bushings haven't been replaced, I'd consider doing that. The W124 and W126 chassis do wear these out and they can cause a good deal of instability at cruise.

I have NO problem believing a dealer would not be interested in correctly diagnosing a drivability problem in a W126.

If you're willing to drive a bit for a really accurate diagnosis, I know a GREAT mechanic in Omaha.

__________________
Steve
'93 400E