... is still weeping, so I've ordered a S/H part with a short guarantee, for some temporary respite.
(I suspect it was my powerflushing last year which caused this and the AAV to go titsup).
Once I've swapped it out, I'll see if I can dissemble it, and replace (or refresh ?) what is obviously faulty - the "O" ring around the valve actuator.
Given that any design requiring a seal around a piston will ultimately fail, I'm curious as to whether it's possible to manufacture a seal-less valve, maybe doing something clever with magnets and springs ?
I am incredibly pissed off, because about 6 years ago, the diverter valve was changed under the British Gas cover we have since abandoned, and I kept it in the garage on a shelf for *ages* ... until I decided to clean up :(
If I had kept it (it wasn't leaking, the actuator had failed, but BG changed the whole assembly) I would have swapped it in and looked at the failing part.