Just a quick update. my eas diaphram wasn't sealing, except when i put my finger over the exposed exhaust port for a few seconds. you nice chaps suggested a strip and look see, and what i found amazed me.
no, not a little gremlin but poking out of the little brass tube beneath the diaphram was the tip of an o ring....... removed it and all is fine.
i can only assume it was dislodged from behind the collet on a previous refurb, and worked its way up to the diaphram.
is this a first.... or am i just unlucky. cheers all, hope this was amusing.:mooning:

It can happen, that is the down side to people refurbishing their own valve blocks and not counting the o rings they take out as well as put in!