You should now carefully unscrew the cylinder end cap making sure it doesn,t fly. With cap undone, the sleeve,guide and mainspring should come out. You may need something to ease the piston out. The piston seal on mine was a parachute seal which looked ok. If it needs replacing you will probably need to dip the new one in hot water for a few seconds before fitting. Clean and lube the gun. Refit the piston,mainspring, guide and sleeve (mine had a small hole for the end cap locating screw to go so make sure if it has one that it,s in the right place) and then screw on the end cap. This may be a bit difficult so make sure you dont cross thread it. Tighten cap and replace it,s locating screw. Replace the long cocking link and then the barrel/breech/shim set up and replace the barrel pivot screw and lock screw. Line up cocking links and replace its pin. (mine was slightly bent because some chimp had fitted a big mainspring). Slide trigger into housing and push down long leg of spring (see pt1) so the trigger can slide into place and then refit its pivot pin. Slide sear into place with the hooks over its pin and then refit its spring. On mine this was a bit tricky and took a couple of small screw drivers although I think some models had a screw you could unwind to get the spring in and then retighten. Drop action into grips and refit the screws at front and rear of trigger guard and refit sights.