Originally Posted by Spider-TW
The early RTs had a rail that didn't support the field strip screw o-rings very well. They have a pretty large chamfer on the side near the valve that lets that middle o-ring loose its seal. Tunamart has the replacement rails, but you might need to contact BigEvil to get it.
As a test, it sometimes helps to put a ninja reg shim under the head of the banjo bolt. This pulls the middle o-ring down that much more. This helped on mine for a while, but I eventually repaired the rail for that particular problem. You could also try a lower pressure bottle (~800 psi) to see if it seals up. A shim and a standard bottle worked on mine, but RT'ing with a ninja bottle would set it back to leaking.
Also, be sure you are using AGD o-rings or 90 duro urethane o-rings on the banjo bolt. The o-rings hold the banjo centered in the hole. If you use soft o-rings, the valve will shoot itself towards the back of the rail, throwing off your bolt setup and making it easier for the banjo o-rings to leak.
It's hard to judge that middle o-ring leak, as a lot of the air often comes out of the back, under the valve.