-WillN - A leak from the middle 1/8 Banjo Fitting quick disconnect (or QEV quick disconnect) can be caused by a bad hose. Remove the Banjo Fitting and make sure the hose end is intact and cut straight. Make sure the hose bottoms out inside the banjo's quick disconnect. Try cutting 1mm off the end of the hose to shorten it up. This will create some tension pulling on the hose and letting the quick disconnect seal up. A quick disconnect will not seal properly if the hose is being pushed into it.
O - A leak from the middle 1/8 Banjo Fitting threads can be caused by a worn out or damaged banjo seal. Replace the banjo oring with a 1.5x3mm oring. Check to make sure it is not cross threaded and there is no debris around the breech inlet port. Screw it in finger tight. If it still leaks, replace the banjo fitting. If using a QEV try using a 08/90 oring or alot of teflon tape. When using teflon tape, do not allow any near the air port, keep it all on the threads.
P - (QEV only) A leak from the QEV exhaust port can be caused by a damaged QEV. Replace it. A small amount of air will be exhausted from this hole during firing when the bolt moves to a closed position. This is normal.
Throw some loctite on it for a giggle and see what happens
I'd Recommend Loctite 243