Damn--lost a post. Anyhow,remove trigger pin circlips and remove the trigger pin and remove trigger and its spring. Remove other two trigger pins and pull out safety catch, sear and sear spring. Place cylinder, end cap down, on a block of wood, with the flat of the cap on the wood and the pointy bit overhanging. Push down and remove pin and release pressure. End cap, spring and piston can be withdrawn. The ptfe piston rings can be replaced with "o" rings but I dont know the size. I replaced 1 ring on a rough gun I had to get it going. clean and lube gun and put back together. Put piston, spring and endcap in cylinder (as with removal) and push on cylinder and replace pin. The breech block can be placed in jaws and located with pivot pin. Depress plunger and spring and push pin home. Replace cocking arm and pivot roll pin. Place sear spring onto sear and sear onto safety catch and put into trigger housing and line up with pins. Push the front two pins through and replace circlips. push trigger spring into end cap and push trigger up until it lines up and push that pin through and secure with circlip. Tighten the adjuster screw on the end cap. Go to next post.