I had an unpleasant surprise when I removed an HR92 head and adapter yesterday - water started to come out, as did the valve pin. Replacing, and screwing down, the adapter stopped the leak but I need to solve whatever is wrong.
There's a thin white plastic ring around the pin but I can't tell whether it's broken off from something inside or whether it needs to be screwed back into the valve body. I can't find a drawing of the valve innards so I'm hoping that someone here has had one apart and can explain.

Also, while looking for a replacement, I see there's a V120-15 and a -15a but I can't find an explanation of the difference ... ?