Assuming you have removed the transfer port insert for a look and maybe fitting a new O ring on it, you will want to get it back into position. I managed to drop it into the cylinder, get it into place and then push it with a dowel. I fitted the piston, mainspring and guide before refitting the loading tap, but I think doing the tap first is a better idea as it might be tight if you have fitted new breech seals. Locate the loading tap and locate and tighten its pivot screw. If the tap is tight, due to new seals, then you can wangle the transfer port insert a little. Once you are happy with it, replace its locating grub screw on the underside of the cylinder. Replace your piston, mainspring and guide/endcap. Put some pressure on the endcap and push the cylinder pin through to locate it. Replace the cocking lever and locate the cocking arm into the cylinder and then put the cylinder onto the diecast frame and replace the 3 screws that hold it. Replace your grips and replace the top grip screw. Swing the grips to the angle you want and then tighten the screw on the underside of the pistol grip. Replace your rearsight.
I have not had a chance to try the pistol since the strip and I guess it will not be too accurate with the crude rearsight. It does however seem a fairly well made pistol. I have not checked the spares situation and did not remove the trigger components, but did notice a little wear on the pins, where the cocking arm had rubbed.