I did it!

[Squinty]

I made one of my E-bay short core regs ..last for three tins of pellets before leaking!!    
Yes the damned thing started to leak through the breather.
Stripped, polished, rebuilt the POS, set, tested and back on the gun.

Other than it possibly not liking a 220/230bar fill? I still can't work out exactly why it springs a leak.
That is unless as Kev has said there is burr that I've missed that only catches when its fully discharged. ie the bottle comes off and goes back on again.

[KevG]

had that problem with a theoben reg,had so give the internal bore a really good Polish were the larger of the two orings sit
kevG

[Squinty]

had that problem with a theoben reg,had so give the internal bore a really good Polish were the larger of the two orings sit
kevG

I chamfered the top & bottom of the bore, just a twist. andgave it a good mopping with autosol
Wthe anoying thing is the core is set with 0.3mm float basically there is so little travel the o-ring barely flexes.

Been meaning to ask have you got any 0.6mm belvilles that you can spare?
Enough for a full size reg?