Following help from Pete (p.j.) I sussed how the trigger components go back together and subsequently also how to strip the rifle and remove the piston without dismantling the trigger. All good experience.
I have new seals for the rotating breech and a new piston seal on order.
When taking the rifle apart (.177), the steel spring guide was in two parts ... a tube and an end washer. The washer was prevented from falling off the end of the tube by very crude belling of the tube. My first thought was that the washer had been fixed to the tube but looking at parts diagrams indicates the guide is in fact 2 pieces. Again, you learn. The guide was a pretty loose fit in the spring so a new delrin guide has been made. the spring as removed is 250mm long, 3.2mm section wire, 33 coils, 13.9mm id but I guess this could be 14mm in reality. The spring has plenty of room in the piston body (rattling around) so a PTFE liner is now fitted, as is a top hat.
A puzzle has been what I can only describe as a big home made top hat or front fitting guide: at first I thought it was a standard component as it is well made but now very much doubt it. It consists of a steel rod maybe 9mm diameter with a steel flange about 3mm thick and the same diameter as the inside of the piston at one end. The rod is almost as long as the piston inside. It would certainly add a lot of weight to the piston! I can only imagine it was added as part of a home tune??? I will leave it out when I do the rebuild. I could now kick myself because now I know this steel rod is not standard it would have made making a delrin guide so much easier as there would have been no need for a central hole for this steel rod to fit inside in the guide. Well, once again you live and learn.
Other data: front stock screws M4. Trigger guard screw and the Maxi rail screw 2BA.

All I want now are the breech seals ...
Cheers, Phil