Having just replaced my 2.1 TD partly because of a slipping (but very light) clutch, the one I have replaced it with had a very heavy and rather sticky clutch, but at least it didn't feel as though it was about to fail, so I tried what the average non mechanical person would and ran some oil into the top bearing of the operating shaft in the bell housing. The result I can only describe as dramatic, the pedal only needs about one third of the original pressure and engages much more smoothly. I cannot guarantee that it will improve them all but it certainly did mine.
Peter.N.