Fuel Lube, and tighten them like tapping threads.
I use fuel lube and have no leaks. Unless they match up perfectly in orientation the first time you tighten them, which is rare, you will need to "work" them into position. This is done by backing them off a quarter turn, then tighten, then back off, then tighten, just like when using a tap for threading. You may need to remove them and clean the threads, then try again. Once you get it into position do not back it off or it may leak.
You may find a fitting that will not allow you to get it into position. Try another fitting. They are not all machined alike.
Smart People do Stupid things all the time. I know, I've seen me do'em.
RV6 - Builder/Flying
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.