To give you an update on the problem, I brought the car in and the air-fuel mixture was running a bit too rich. That was adjusted and it ran a little better. However, the vibration was still there. More inspection found that the engine mounts were shot. The driver's side was approx. 2-3 lower than the passenger's side.
Now that the car has new engine mounts, it drives like a dream! I cannot believe how much of a difference engine mounts can make. The mounts have fluids in them to help dampen the engine vibrations, so if you see any fluid leak on older MB, u might want to take a look at your engine mounts.