Perhaps it is leaking through one of the two valves. I don't know if you could fix that, but it is definitely leaking somewhere. It's obvious (by your water test) that the leak is not in the bladder/pump setup. It must be leaking after you pull the trigger, which means the problem could be in the valves, tubing after the valves, or piston.
Maybe you could try to listen closely when you fire it. Try to listen for air rushing out somewhere other than the end of the piston.
Edit: How fast is the ROF? Is it slower than after it stopped working well?
Edited by Vintage, 28 August 2004 - 09:28 PM.