I've visually checked the motor mounts and they appear to be in excellent shape, easily over the 12mm gap you suggested. The only indications of driveshaft problems are the vibration around 80mph and the gearshift from 1st to 2nd is a little jerky. Most other conditions the car is very smooth. I am going to replace the flex disks and center bearing to see if that cures the problem. It looks a fairly straightforward job to do myself. I'm now pretty sure this is the cause of my problem, I'll let you know what happens. Again many thanks for all your help.
Colin

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92 Mercedes 300E 2.6
86 Plymouth Conquest TSi
79 Chrysler Cordoba (without Corinthian Leather!)

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