I used a foot pump with a bit of wet rag to seal the adapter and put it in the transfer post and managed to blow the head back far enough to wangle it with a dowel. (same trick worked on scorpion). Piston washer is an "o" ring. I replaced a buffer washer with two bits of leather (not worth the hassle but I was curious) and have used a tap washer in the past.Clean and lube. Slide piston buffre and its washer onto piston head and insert into keyhole of piston and it should snap into place although you may have to file small chamfer on one side of washer. With circlip set up a piece of tube to push clip on would help but Ive done it wirh two small screwdrivers. Place piston, spring and guide in cylinder and push down with your piece of tube and refit pin. It is worthwhile changing breech washer as it is made of same stuuf as piston buffer. I make leather ones. Place brech in jaws and fit plunger and spring,depress and fit barrel pivot pin. Fit trigger stop pin (tape on left side of trigger housing stops them falling out) then offer trigger,spring and sear into housing. Locate sear and fit pin and then trigger should push up to enable trigger pin to be fitted. Replace plastic cap and refit in stock and fasten screws. ( if you adjust trigger at all, 1/2 turn of the little screw in plastic in the trigger can stop the sear from engaging).