It is my experience that shaking above 80+ is always tire balance related. Often, if you observe closely you can see it in the dash and steering wheel if it is the fronts.
Rear balance problems sometimes can be observed in the interior review mirror and seat backs bouncing.
If you don't experience this other than high-speeds, tire balance is where I'd start. Make sure you go to a place that has a newer balancing machine.
I just noticed that we are getting a shimmey in the steering wheel of the 190E at around 45 mph only after going over a bump. I suspect it is a worn steering damper.
Keep us updated on what you found.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)