I am not out to make enemies or fall out with anyone. However, I must question your logic again. My own clutch pedal on my Spider was sticking down. I too had to pull it back up by hand. I did not change my Slave cylinder but I did do what you too would have had to do as an incidental, I changed my fluid. I have had no problem since. There was no leak of oil so I KNEW that the slave had not failed.
The experience you outline ( sticking pedal ) has nothing to do with the problem the OP has. Sorry.
As far as rubbishing my theory that wear in the clutch itself can cause a heavy pedal, well, sorry, but again you are wrong. Check out Simon above who says they do tend to get heavier with age, that is due to WEAR, just as I said. Sorry.
The diaphragm spring in a clutch is operated by a release bearing, which is in turn operated by a pivoting arm which in turn pivots and is operated by the slave cylinder. Every pivot point, bracket, location or sliding element in that system can wear, bed into a groove and become stiffer.
I have experience of clutch spring fingers breaking off, causing the thrust bearing to go skewiff and it started binding on the clutch as it moved forward. How did I find this? The pedal was heavy, and actually there was a whine from the thrust bearing too but that's beside the point.
I don't mind batting this backwards and forwards as many times as you like but it will not alter the fact that the problem is not slave and it is not fluid condition. Which just leaves the expensive things, unfortunately.