There is a small 'o' seal in the breech block where the probe pushes into. This may well have worn giving you the breech leakage. Pull the cocking handle fully back and lock it down then shine a torch into the breech hole and you will see it.
I remove mine with a straightened paper clip with a small right angle bend into the end of it. Ensure you smooth and round off the end of the wire before you use it. I cannot remember the size but once removed it shouldnt be too hard to get a replacement. It is fiddly to do and just as fiddly to put back in
Alternatively contact Falcon at:
Falcon Airguns
Unit 5-6, Hailsham Industrial Park,
Diplocks Way, Hailsham,
East Sussex BN27 3JF.
England.
Tel:: 0845 6588616
and talk to Mr Cooper and arrange for the gun to be serviced. About £30 if memory serves but the gun comes back in top order. There may well be damage to the valve if previous owners have over zealously tweaked the hammer spring but the service will sort that out.
AA field work very well in these guns. Least ways they do in mine. I have had no problems with them clipping the breech as the probe locates the pellet. A problem I did have with Accupells.
11.5 ftlb with AA field is very achievable and you should get over 32 shots(4 Mags) at that level. You will need to find the heart of the fill which in mine is a 150bar fill.