Trigger valve was leaking on frame nailer, also slow leak in main cylinder
Drive retaining pins from trigger and trigger valve. Remove trigger valve and replace. Be sure to grease new valve before installing. Replace retainer pins and trigger. Then for the main cylinder, remove the head and pull cylinder assembly out. Inspect for damage, replace any 0 rings that need it or lubricate them. Reassemble the cylinder and insert back into gun. Grease head gasket and replace. Pressure test and fire the gun. Make sure nails are advancing and no air leaks. Good to go!!
Assuming you have removed the trigger arm and removed it. to remove the trigger arm only take #6 finishing nail cut the sharp end off to make a small punch. Then using this nail and a lite hammer remove the tension pin clear trigger and put trigger and pin in a small bowl place in a place where you will not knock it over for pin tends to blend with the surface is hard to find. Then look at the valve on the handle side you see another tension pin use your punch you just made and remove the second pin. Assuming that the old valve is no longer operational use average pair of needle nose pliers and grab stem and pull with steady medium force and remove valve.
To replace new valve.The new valve will have a flat side so you can line the pin guide take your punch line up the pin channel and replace the pin using your punch as a guide. Then replace your trigger. Make sure you use the grease provided with your repair kit with your valve then replace trigger and you are good to go > remember do not operate gun any higher than 100 pounds psi