I'm very glad you solve your problem.
I'm not sure if a machine like that is available in Portugal.
Regarding the transmission shaft I think that a 500 will damage it sooner because of the higher power and torque, in my case I had no chance unless replace it.
Well I think I already replace every thing in this car...
It should be an interesting point of discussion... W140 owners repair list..........

How can we test the trans shaft? I continue to feel vibration all over, even when I'm on the freeway and the car is in neutral.


[QUOTE]Originally posted by Folgado
[B]"Secondly the vibration is still there when the car is "rolling" with tranny in neutral... "

The gearbox disconnects the engine from the shaft not the shaft from the back wheels!!

When you are rolling the transmission shaft is rolling as well.

YES the gearbox is different from a 93 to 95 S500, but the shafts are exactly identical.

The trans shaft only last in decent shape for 200.000 km, and if you run with the engine mounts dead it will go bad much sooner.
QUOTE]

I Had Same Problem With A 600sel And 300 Sl Vibration At 55 To 60 Mph That Goes Away At Higher Speeds

Both Times It Was The Flex Disks Even Though They Looked Alright

It ended up being my motor mounts. Replaced them and everything is like new again.

If the vibration is during acceleration (load) and goes away when you let gas pedal then you can look at the driveline components, but if it is at certain speeds and especially if you feel the vibration in the steering wheel then look at the front wheels alignment and balance. Also for the back wheels check the balance of the drive axels, by suspending the car and running it at the speed where the vibration occurs, loose CV joints also can cause vibrations.
I hope this helps.