Vin you could be right there.... to be honest though I have never had a leak that could not be sourced using this technique the tube amplifys the sound quite dramatically to the point of being able to hear leaks that you cannot by using ear alone, sort of like a stethoscope in effect! I would be surprised when using this method if the source remained a mystery for long. 25 min is ok but odds are it will begin to leak air faster and especially when it matters.

I remember a converstion I had with Tom Cook about leaking air systems and pressure duration, He said "3 months" would be more like it! (He was refering to the gear system in his Firebird at the time) Wow!