I have done all of the above suggestions with my SB 1842bn including replacement parts,including oiling all the O-rings, cycling the piston by hand, and including checking the air pressure plus having the proper nails, and it still leaks at the trigger. I've gone through the gun three times, making sure there are no burrs on the piston shaft. The only thing I can find is that the piston seems to hang up ever so slightly towards the top of the cylinder. After applying more oil it seems to move fairly well. btw - I'm a former machinist so I know my way around a wrench. Now what do I do? Any help would be appreciated. Thank you very much.