Really old thread, but worth an update for anyone else looking for an answer to this. I had really bad clutch judder on my is200, which had had a clutch replacement before I got it. Fearing the DMF was worn, I avoided the bill for a while and just got used to driving it as it was.
My car later developed a vibration at motorway speeds and I diagnosed this as the prop shaft centre bearing mount having too much movement in it.
I bought a new mount and went to fit it, but noticed that the new mount didn't feel any stiffer than the original one. I did however notice that there is quite a bit of adjustment built in to the two mounting bolt holes for the centre mount, and figured the prop could simply be out of alignment. I adjusted it to the opposite side of the car from where it was bolted up when the clutch had been changed, and this has completely transformed the car. Not only has the vibration gone, but the clutch judder has gone too.
Problem solved for zero cost, just check your propshaft alignment!
