I use Loctite 567 which is a hi-pressure thread sealant....not just a lubricant....it needs to cure first however....I had a leak in an NPT hose fitting...this cured it....twister
I used something similar, called permatex #54540 pneumatic and hydraulic sealant to seal a ORB straight threaded fitting that was machined improperly, not allowing the gasket to seal. Worked great. I now use it for most all my hydraulic connections. Amazon has it for $26. NAPA charged me $37.
/ Whats the trick to hooking up hydraulics and not having leaks
I use great white Teflon paste. Non of mine have ever leaked. They are all NPT threads. The stuff is cheap and available at Lowe's. I am sure it is not as good as some of the higher priced more specific Hydraulic sealers mentioned here, but it has worked for me on my hydraulic projects.
/ Whats the trick to hooking up hydraulics and not having leaks
Teflon paste sealant took care of 5 out of 6. The 6th one which was the really bad one worked with 3 wraps of Teflon tape. Careful not to have any past the threads and wrapped clockwise facing the threads.