Eventually I've got all the couplings I need to make my compressor work. The threaded parts leak a bit. I don't want to tighten the things up until they bend, so what's the best thing to seal them with. PTFE tape or some goo of some sort?

PTFE tape, 2 or 3 wraps, make sure you wrap it in the proper direction.

Yep PTFE tape is fine, 3-5 wraps applied clockwise is the official recommendation.

Davie

Locite "Loc n Seal" works wonders.

PTFE works for me

yeah, it is a pain innit - as you say, you don;lt want to tighten too much is case you split the alloy.

I made rubber washers from bicycle inner tube.

I used PTFE tape same as the guy I bought the compressor from and hes an Official Sealy repair agent.

If its good enough for him its good enough for me