Clutch problem

[joe90]

Been threatening to do the clutch on the 100 quattro for a few months now, anyhow a mate turned up on sunday and we got on about fitting the clutch, he told me to get in the car start it up and pump the pedal a few times to get preasure and then try the clutch.
After about 8 pumps i tried selecting first and hey presto it selected great, as did every other gear, took the clutch to biting point in every gear and it wanted to drive so nothing wrong with the clutch, tried it again tonight and took it for a drive and it drives ok.
Anyway my question is what would make the clutch stop working correctly all of a sudden and then start working again with a few good pumps, i have no visible leaks of fluid, could it be air or dirt in the system, or are the hydrolics known for any common faults?.

Thanks Bryan