my job title is clutch actuation global core engineer (or something)
if you pull the pedal back up does it sit at the top again? if so then there is insufficient return force to overcome the over centre spring. the OCS pushes against your foot for about 25% of the travel and then helps you for the rest to reduce the pedal load. if some air has got into the system then there wont be enough push to push the pedal all the way back up.
if the slave cylinder is leaking then there might be evidence underneath – go and have a grovel underneath so see if you can see anything. i dont know if vag use concentric slave cylinders or not – if they do the gearbox has to come off:(
if its the master cylinder primary seal then one way of checking it is to apply the clutch pedal fully stick it in first and with the engine running see if the car wants to drive off after a few seconds – if it does this means the primary seal is leaking and you need a new master cylinder. you wont see any leaks as the fluid is leaking back past the primary seal and into the low pressure pipe.
if the secondary seal is leaking you will have a wet foot.
if it is not the actuation system it could be something wrong with the clutch mechanically – something broken such as the spring or the pivot or something.
one thing i have discovered is much pumping of the pedal to try and evacuate the air can sometimes fix your issue temporarily. what happens is some air escapes out of the low pressure pipe and the rest gets smashed up into microscopic bubbles and the fluid acts as if there is no air in it. come back in the morning and lo and behold the pedal falls down again.
first thing to do is the check the fluid level and then do a creep test if the clutch still disengages, and then get it bled if you can. does pumping it say 20 times make it feel a bit better? if so its almost certainly air, if not it might be clutch cover related.
