Thanks Dennis, yes I know it is not rocket science (NASA! ha-ha!

), the valve-block is a very simple thing really, much maligned by its antagonists but a mystery valve-block leak is totally baffling (it is not the airlines - I bought 50 feet of airline and ran new direct lines everywhere - made no difference whatsoever so I connected the original ones back).
The mysterious thing is that every time I rebuild it it leaks in a different place (or rather the pattern of collapse is different) which by deduction leads me to the conclusion that whatever I am doing with the valve-block is making it leak in a different place.
I always have different volumes of air leaking around the solenoid covers - it seems the o ring is not doing its job (could they be thicker?) either at the valve stem or the valve base. The stem solenoid is a 'moving' seal so there we are entirely at the mercy of the o-ring and its seat (an area where you say you have seen small cracks which I will inspect this time) but the valve base to metal seal is possible to 'enhance and assist'. The original valve stem seal is a vinyl sleeve which looks fragile to me and as if it would wear fairly rapidly - in your kit you replace it with an O-ring yet it is so small I wonder if anything could be done to help that seal?
However, the fact that the reservoir empties in several hours leads me to suspect that either the non-return valves are not sealing or the diaphragm is leaking (although the car pumps up readily which negates the diaphragm I think?) and those are the areas of 'leakage" I am most concerned in 'assisting'.
I mean if you think about a tyre or bicycle valve the principal is the same - the pressure of the air assists in making the seal on a rubber or vinyl seat, so why is it so difficult for me to make my valve-block stop leaking?