air leak after installing RT

ok... i just bought a response trigger and love it!!! its great! but the problem is whenever i put air on the gun i get a little *psssshhhhhh* noise. i put my ear up to the part of the gun with the valve on it. its the loudest there. so im thinking great. something is wrong with my valve. so i took the gun apart.. checked it all.. loctited all the stuff that needs it and put it back together... still no luck. so i take it apart again. and look at the valve. on the inside, the valve seat o-ring isn't in the best shape. so i looked up all the ways to take the valve apart and think i can do it.  but the thought of me taking it apart is not one i like so i double check myself. i took the side of the gun off and put an almost empty tank on it so i could see the internals while it was aired.  i could hear the air better . i put some soapy bubbles on the front bolt and what do you know they blow away... so its the air is coming out of the valve.

so the thing i would liek to know is...

1.) besides the oring that is screwed up, is there anything else that could be wrong?? the last thing i wanna do is take the valve apart

2.) if i do replace the oring, what size is it? does it come in the replacement parts kit??

thanks to all who help out!!!!!