The owner said he would spend some money on it, so I dismantled it, measured everything up, sent the dimensions off to Ron Young. After a week or so, new spring and piston washer installed, not exact sized parts but close enough to work. Breach seal is an odd ball size and haven't found one yet, so original still in place.

It's shooting with some reasonable power for its size now.

A mate has had this since he was a kid, many decades ago. 

It wasn't firing pellets out, the piston moved forward and I could hear gas escaping, but not enough to fire a pellet. 

Disassembly didn't go easily, a very particular clamp is required, which I don't possess, of course, so after some time, loss of skin and even more cross words, I got it apart.

The problem was the trigger block, the main spring has to be compressed in place to move trigger block forward into the main tube and lifted out the trigger hole. With very little filing, the trigger block was made to come out the end of the tube with the main spring, perhaps it was never meant to come apart after manufacturer.  Anyway, I now had it in pieces. No leather washer, it has a PTFE type, everything looked ok, except the cylinder tube was all gummed up. The piston washer has hardened, the breach o-ring isn't flash either.  

Cleaned up everything, including the barrel, which probably hasn't been cleaned in decades either. Reassembled.

Its working now, although power is fairly low, claimed to be 540fps new, don't think its anywhere near that now. A new piston washer, main spring and breach seal would make a difference.

Surprisingly, my youngest really likes it, light weight, easy to shoot, and looks sporty. 

I'm not a fan of it, but it does shoot consistently