Vic;
Loctite makes a thread sealant specifically for NPT threads. #565. I don't know if it really matters that much but they went through the trouble to manufacture it. Also I would recommend the primer. It made a difference for the times that I used it. It has some chemical reaction that facilitates the success of the anaerobic activity of the sealant. The 545 may work just fine. I would use a "dry" solvent like acetone or Wally World brake cleaner to clean the fittings first. Good Luck.
SimS
I picked up the 545 at Grainger; it was the only place I could find it. I didn't see any 565. I think the 545 should do the job. If I can find the primer today, I'll get some. The brake cleaner also sounds like a good idea. Thanks.