My premier started to play up - it would sometimes discharge slowly and not fire the pellet. On dismantling I found the piston seal had become very tight. However, it looked in nearly perfect condition still. I understand that the blue piston seals were fitted to the later mk 1s. I tried to buy a replacement but could only find the earlier white seal which is about half the depth. So, I used some emery cloth to reduce its diameter, lubed etc. and it seems to be performing fine.

I was told that the blue seals can expand and also read elsewhere on this forum that they are not good. So would be interested what people suggest (if anything) to replace it?