I ran into that issue last year when I was putting my T/A together. My lines were leaking like crazy at the carbs, and nothing seemed to help, until my engine builder told me to put some grease on the threads before installing the lines. I never thought that would work, but was running out of ideas. Greased the threads up with red grease, installed and tightened them, fired up the engine, and dry as a bone!
Grease or oil is best and should always be used on flare fittings to allow you to get them tight.
IMO never use teflon tape anywhere on a fuel system, never. Because it is near impossible to get all the little pieces out when you take it apart. Plus it looks like sh!t and tells everyone you don't understand flare fittings.
