Hi, another $0.02 on this thread. Get someone to observe your slave cyl. in 
action, when the pedal is depressed. DIY by tieing a string to the arm, and 
hanging something off it. If all apears well, and bleeding didn't work, and 
changing the tranny oil also didn't help then I'd begin to wonder about the 
pilot bearing the the input shaft rides in. This will produce the symptoms 
you describe also. It happened on my '85 at 95,000 miles/6 years old. Mail 
me for the bearing removal method, once you have dropped the tranny! The 
bearing is cheap, $<5.00, from a non VW supplier.  tim s.