[Mike Arnold]

I agree with the other reply that the pair of rubber prop shaft mounts are important to cut down vibration. Many years ago I had a knackered engine in my 122 which leaked oil. The oil sprayed the underside of the car which, although it stopped rusting, made the the rubber mounts go soft and encouraged vibration.

One other thought: check the universal joint in the propshaft. If there is any play that too can cause vibration.