Stripped it, cleaned it, rebuilt it, still a very very very weak leak. Unless you put your ear to the feedneck, you cannot hear it.
The 2 x 015 orings on the valve body I tried to replace as that is probably it, but I think the original ones are 90x015 and not 70x015 which I have from my Vanguard days... so they feel too loose on the valve body.
Dropping down to 014 and the valve slides into the body too easily, so not sealing so I put the originals back in.
Dry fired it, seals again after a shot so no leak until you degas and air up again.
Now, I am putting it down to 4 things;
1) Bottle was reading 500psi (but probably actually less than that - my bottle is set to 550psi) so pressure isn't quite there to seal the gun.
2) It wasn't leaking when I had the bottle set to 850psi - no spare bottle to test it.
3) Might need ram and ram housing stripping and cleaning. Solenoid may need cleaning too (Aaron @ FS suggested that) but no precision screwdriver so couldnt do that.
4) As I changed from 850psi to 550psi, I did not balance the HPR and LPR. I have no chrono here either - going by feel more than anything - so it could be that they need balancing.
Board was reset before I noticed the leak too - so maybe dwell needs increasing? Currently on 16ms, I think.
The leak does not affect performance of the marker. As I said, it seals on 1st shot and stops leaking. It is probably something VERY simple - but i've now run out of air dry firing it.
So reducing from £275 down to £215 inc delivery.