[Formulajones]

Using Teflon or any kind of sealant on a flared fitting will do nothing to seal the flare. If you have a leak it's because something is wrong with the flare, the threads don't do the sealing, and when it leaks past the flare, if it doesn't come out of the threads it will just come out behind the nut between the tube and the nut.

Most of the issues I've seen with flares is using the cheap seam tubing from the auto parts stores. Sometimes they just don't flare very well, especially if using a cheap flare tool. Seamless tube is better but harder to find and more expensive, and of course a good quality flare tool does wonders.