Flared fitting or sleeved? What kind of tubing, copper, aluminum?
Flares can be real easy to make a bit off center when using something soft, so one side of the flare may be thicker than the other leading to seepage. You could crank on it till it squishes out, but with brass fittings that's not an option.
Teflon wont fix it as you'd need to put a fair amount in the tip of the fitting where the flare contacts it, and that opens you up to getting excess teflon inside the lines. I've also had issues with the teflon just falling apart on contact with fuel.
In my experience with varios types of lines, it's usualy better just to lop off the flare, ream the inside a tad, file the end square, and try again. If you're using compression sleeves, pretty much the same advice. Now if you're using the good type that cut into the tube as the B-nut is tightened, those are one time use so you'd need a new sleeve as well.
1956 GMC 370 dump " 'Tater "1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI
I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P