I have a 1990 Sierra 1.8 CVH which I have had from new ( yes that's 13 years ) and I have had three new clutches in it over that time. The last one was 12 months ago and now it is juddering badly again which has the been the problem with the others. There is obviously something causing this to happen. Any suggestions ? Could it be the prop shaft out of balance, flywheel buckled, cush drive on the propshaft weak? The car has done 79,000 miles.