Also look at your trigger sear, there is a threaded rod on it, this is used to time the sear release and the on/off valve actuation. If this were to be adjusted too much in one way or the other it would cause a leak down the barrel or bolt stick with no bad o rings. It should be adjusted so that there is about 3/16th inch of trigger pull before the sear is released and the gun fires.
If this is not the issue, check the power tube o ring (and spacers if lvl 10). After this issue is cleared, if it still leaks, remove tho on/off valve assembly, the o rings should be bright white. They are also teflon which means that if theyre stretched they will not return to their original shape and must be replaced. Check this by fitting the o rings around the on/off post. It should be a fairly firm fit. When reassembling the valve there should be instructions laser etched right on the valve, follow these and you should be fine.
If you need o-rings check AGD's official website. Just remember to get the right kit.
If I remember correctly you may need to phone in the order, its been a while since my last order though.