Lathe suggestions?

[Neale]

I would normally expect to see a head with a machined seating which bears on a matching machined flat on the bottom of the carriage, plus fibre washer. Clearly here they seem to expect the threads to seal. If PTFE does not do the job, then it might be worth trying Loctite 55. I've had a lot of success with that on household plumbing - typically the screwed fittings that go into the bottom of radiators that also rely on the threads sealing. I've had first-time success with every one of those, where using PTFE has been less reliable. Might be my technique, but I'm sold on the stuff. Can't see that it says anywhere that it's good for oil - just potable water and LPG - but I would probably give it a go.

Out of curiosity, what oil are you using?