Yeah, mine has a leak on the power cylinder, I could hear it if put my ear right next to it when running. Didn't lap the piston or the cylinder, the piston had an amazing finish straight from the lathe so just left it! The cylinder wasn't too clever though, I tried to ream it with little success, so really it wants a new cylinder making and lapping to suit the piston, that'll probably be easier than making a new piston.
It'll probably also leak around the displacer rod as I damaged it when gripping in vice to tighten (silly boy ... well I was in a rush to see if it worked!) so when I got rid of the burrs it's now probably a bit smaller than it should be. Also think because of that the displacer is catching the wall of the hot cap slightly, there is slight scraping noise now that I couldn't hear before.
All of these things definitely aren't helping my cause but I don't want to spend time making new components really, I could be on for ever and would probably re-do the whole thing if I started that!
I want get it running acceptably for a short demonstration with cold water in the jacket and the meths burner, then move onto the next project!
Just bought a new XJ20 milling machine from a guy on ebay, looks a pretty decent sturdy machine for the money so that should improve my capability too.
Nick