They are easily repairable.
The sealing mechanism is a spring, ball bearing, and a o ring rubber which is shaped to form a figure 8.
You will find that an accumlination of crap has worn out the o rings.
I just turned the o ring part over , gave the spring a bit of a stretch, everything a good clean and re assembled using M4 screws and nuts. Using new o rings would be better but I didnt have any at hand.
The tap now holds OK, so there is no rush to buy a new one.
They are only £18.50 here in the UK from Lings.
_________________
Russ
MC21SP