Try checking the flex discs on the propeller shaft. (Substituted for U-Joints on a drive shaft) After 100,000 miles, the rubber has a tendency to start to come apart. Posts show catastrophic damage if left unattended. A common sign of problems is vibration at highway speeds.
One other thought - if you have recently lost balance on a wheel from hitting a curb, or tires are worn down, these could cause symptoms.
A mechanic friend of past once told me that tire vibration makes the steering wheel vibrate, but if you feel the vibration in the seat (or in your crotch), its probably the drive train.
At 60mph, the tires are putting 10 to 15 hertz (HZ) of vibration. That's reasonably fast, but (and I don't know what your differential ratio is) referencing the Rolling Stones and their 409....the drive shaft turnes 4.09 times for every turn of the drive axle. I'm guessing MB's use somewhere around a 3:1 or 3.5:1 ratio which at 60mph would have the vibrations anywhere from 45Hz to 60Hz. Although it may be temping now, it matches the frequency of your home power. So my question is what kind of vibration frequency are you exhibiting?
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