I recently changed the clutch master and slave cylinders on my GTV 3.0. Strange clutch behaviour is typical of a failing master cylinder. You might have a problem with air which needs bleeding out. I would suggest you start by changing the brake fluid in the clutch hydraulics and see if this makes a difference for a while.
I also have a P2 GTV T-Spark that I am recommissioning. The clutch pedal is set stiff but it has moved half way down and is stuck. I had all sorts of weird experience with the 3.0 before the master cylinder gave up. So I'd suspect clutch hydraulics and that the master cylinder is on its way before worrying about the clutch plate itself etc. You can pull back the rubber on the slave cylinder to look for a sign of a leak at all there, but my money would be on the clutch master cylinder. Good luck.