Does the vibration get worse on accell/decell? or when turning the wheel?
Does it feel to be in the wheel or in the chassis (between the seats)?
I would have a tech look into it. The thing that comes to mind is a bad front flex disk or possibly a center drive shaft support and/or bearing. The possibilty still exists that you have lost a wheel weight.
Let us know what you find out about this problem.
14 year MB tech
7 year shop foreman @ independent MB/Volvo shop