symptoms are, shudder when engaging clutch (letting out the pedal) , slip, when the engine rpm increases with the clutch engaged (not wheel spin) or extreme travel (pedal almost all the way up before it engages.)
I believe shudder can also be caused by oil residue on clutch surface, caused by some fairly large oil leak, from engine area, dripping into the clutch. Will go away after gasket is fixed, eventually. This happened to me (on another car).
The Cartalk guys from NPR suggest this as the "definitive" test for a slipping worn-out clutch. I haven't tried it, but it'd be fun to watch. This is taken from their website Car Talk
RAY: But here's the test. Find something that absolutely won't move -- like, for instance, the Chrysler Building.
TOM: Pull your car right up to it, so its front bumper is touching it. Then put the car in fifth gear, give it lots of gas and slowly let out the clutch.
RAY: If the clutch is good, the engine will stall, no matter how much gas you're giving it. Since a working clutch connects the engine to the wheels, if the wheels can't turn, the engine will have to stop, too. And we know the wheels can't turn, because we know you can't push the Chrysler Building with an '88 Civic, right?
TOM: If the engine keeps running, then we know the clutch must be bad. Because if the car is in gear and the engine is turning but the wheels are not, the clutch has to be slipping.
RAY: By the way, just so you know, William, a clutch for this car in Manhattan is about $1,000. Plus another $200 for the ticket for parking on the sidewalk in front of the Chrysler Building.