This is posted for the wider interest of the community. I hope it helps others.
First, a summary of the problem - My 2007 E350 has vibrations felt in the seat and in the steering wheel originally between 65 kmph and 85 kmph. I have spent $3500 so far in getting the problem fixed but without full success. Before I state what has been done it is important to grade teh scale on the problem - on a scale of 1 to 10 with 10 being bad and one being a really smooth vibration free drive - the car was at 10, really bad.
What has been done - progressively I changed the two engine mounts and transmission mount ($1145 in Australia). This eliminated any minor vibrations at idle. Car now very smooth at idle. It never was a problem at idle. I then had a new set of OEM Continental Comfort Contact 1 tyres (225 / 55 R16 95W) @ $980 for a set. I then paid $70 to have the wheel balanced and another $90 to have them Road Force Balanced on a Hunter machine. I then paid an addtional $1050 to have the Flex Discs front and rear of the drive shaft changed to try to eliminate drive shaft vibration that I thought was causing the oscillating / buffeting vibration through the seat, steering and felt in the cabin (the resonance was giving me a headache). All of this has resulted in the vibration still there but not so bad (about 5 on the scale of 1 - 10). This has got the main dealer (who were pretty useless) and my Indy guy (who is very good and trust Worthy) really foxed. They too agree the vibration still exists. All suspension components, bushes and linkages in control arms etc have all been tested and shown not to have any problems.
Tomorrow, an independant tire place is going to loan me a set of Michelin Pilot Sport 3 (OEM for C63 and E63s) to try out even though they have tested my Contis and were unable to detect any problem with the tires. If this eliminates it (not hopeful) then its cost me another $1280 for a set of 4).
If this does not work, then I have recourse I believe to two final options - the first is a transmission service form the same place that rebuilds and services transmissions for the MB dealers including Audi, BMW and Volvo. Price for this - Diagnostics @ $250 and Services $400 to $600. The second is to get the drive shaft looked at and balanced $350.
For those of you wondering why I don't just sell the damn car - well I believe it is entirely unethical to lumber some other owner with this problem and secondly, as an engineer, I am stupid enough not to just give up !!! until I run out of funds..which will be very soon....
Watch this space... who ever said that Vibrations were the most diffcult problems to solve was spot on. What price a Mercedes !!! Probably my last one. A pity, cause for 25 years I have driven these... they are not what they used to be.
For those "elite" and experienced members here, perhaps you could respond and same me those last few thousands $ I am crazy enough to spend. MY appreciation in advance for your assistance and wise counsel.