A friend of mine had an HW100 with a leak. I volunteered to replace the crush seal in the breech block, the little bu99er which does seem to fail every year or two. Stripped down his gun, fitted a new seal. Put a bit of air in the cylinder, connected and HISSSSSSSS... It was leaking. Took the block apart, checked and cleaned everything, but it back together and HISSSS... Still blooding leaking! Same process again - same result. I surprised myself with my fluency in the Anglo-Saxon language! After six seals, an awful lot of air and a great deal of profanity I sussed it... There has to be over 75-80 bar in the cylinder to make the seal work! I was just putting 35-30 bar in the cylinder! Hey bloody presto, job done! I am just posting this to help any other silly sod who likes tinkering!