Ceeray is probably correct but I have had a leaky Xicoy valve. The valve actually consists of an aluminium sub plate and two subminiature pneumatic solenoid valves each held onto the sub plate by two very small Phillips head screws. These screwheads are under the silver foil wrapping over the top of the valves. I prodded with a screwdriver to find the heads and tightened them and bingo the leak stopped.

worth a try once you’ve eliminated the cylinders and piping as the source of the leak.

Malcolm