My car failed it's mot because what looked like a large union in the line to the rear was wet, as was the surrounding area of the car and it's taken the paint off . I checked everything was tight, cleaned it off and left it for a couple of days, looked again today and it as wet again. Took the 'union' off and it looks like it's pressure reduction valve. It flows one way (away from the rear wheels) and I can see a ball bearing in there and I presume there is a spring behind that.

It also has a 'blow hole' on the side of it covered by a rubber band to keep the dirt out. I think this is where it's been leaking from. Question is why would it be leaking through this 'blow hole'? I take it it's not a normal mode of operation...

:cheers:
Iain