I have a 560sl with a very noticeable vibration that I can feel strongly in the drivers seat and somewhat in the steering wheel at 65mph. The car has new tires (oem dimensions), an alignment, and tires have been balanced 2x by an independent shop. I've played the game of moving the wheels from front to back with little change and even used the spare on some suspect wheels which didn't help. Don't believe that it's the drivetrain since car vibrates while in neutral and I've inspected the flex disks and they seem ok.

I must admit that I had a somewhat embarrasing moment this spring when I drove the car for the 1st time after a long winter. Apparently the RF wheel was not appropriately torqed and almost came off while driving. I actually heard banging especially when turning and some of the lug bolts fell off in my driveway. I thought this wheel may have been damaged and swapped it with the spare, but the vibration didn't go away. Any thoughts as to what might be the problem?

Thanks!