1983 300D 187000.
While out for a drive today, my wife commented that there seemed to be a vibration coming from the bottom of the car. At about 50/60 mph one can feel a vibration in the drivers side arm rest and a little in the passenger seat. I recently raised the tire pressure to 34 rear 32 front for various reasons. I accelerated to 70 mph (it a looooong drive), slipped the tranny to neutral and the vibration remained. Could this be just too much air in the tires or should the center drive shaft bushing be cheked? How is the drive shaft bushing checked? If it needs replacement I'll do the pair of flex discs too. When removing the driveshaft is it important to mark it in relation to how it was attached originally, i.e. is the drive shaft balanced while in the car? Is the bushing, flex disc replacement project a ridiculous undertaking laying on the ground? Is it more than say, $750.00 to have it done at an indy?
Hate to farm out work but 30 degrees on the ground for a few hours I'll never move under my own power again :-)

Thanks for any advise.