Something isn't just "breaking" during flight causing the masks to leak. (Altitude or pressure change could be accelerating a slow leak) But they either leak or they don't when O2 is armed. AND, O2 doesn't actually flow to the cabin masks until you manually select them to on, or the cabin alt press switch is tripped. ( So your leak is between the pilot/copilot masks and the bottle. Cabin masks should remain in the auto position until the ep calls for something different. What is the sn? If you work for one of the big 3 medivacs, they should all be able to remedy the write-up of " O2 bottle leaks down to 0psi in flight"