Thank you. I am glad that I got it working after a long time. When I took piston out the old leather seal had all but lost its contact with the chamber and removing it proved a difficult job. I couldn't get the retaining screw out first. Then I heated it thinking that it might have been loctited in then it sheared while I was trying to unscrew it. I had to put the piston on to my Taig lathe and use an expensive 4.00 mm Carbide end mill in the tailstock of the Taig and just mill the broken bit out. Then I used a 5mm machine tap to retap the hole to 5mm. It all worked out in the end. I wonder if you advise replacing the leather seal with one of Delrin. I have a stock of 30mm diameter Delrin that I could use. BTW that Oilon was one of worst engineering plastics that I have ever machined.

A.G