Yes, as has been suggested, go through all the unions. It is difficult to overtorque the British fittings, but if they are having to be overtightened, it suggests a problem with the pipe.
Cracked flares are common, and will allow pressure to leak. Vampire has a lot of aluminium pipework, and this can lead to problems. Fittings are easy to obtain (
www.lasaero.com; ask for a catalogue), but the flares are 60 degree, and very different to the American ones.
Common faults in a British air system:
1) Charging valve - though this has probbly been adapted for American use.
2) Pressure regulator - doesnt usually leak on the pressure side, but it can. Can be overhauled - let me know if you want a manual.
3) Air bottle - leaks around the end caps
4) Brake bags - if you leave the a/c with the brakes on, does the pressure drain away?
5) Other components - the canopy seal and canopy operating jack run off the same system. If they have problems, the pressure will drain away.
6) The brake valve can be troublesome, and the brake pressure instrument can leak as well.
A well maintained system wont drop any pressure at all.
Bruce