Like Gerry said, sounds like the double flares were not done properly. With most inexpensive universal double flare tools, quite often the flare tends to not be centered, which can prevent the flare from sealing . I have a Blue Point (cheaper Snap On tool), that has a bar with 3 or 4 different tube sizes, and although I have done quite a few double flares over the years, quite often it took several attempts to get a good looking, centered double flare. Several years ago, I bought an inline flaring tool, which works so much better. No more 2 piece split bar with multiple sizes, the inline tool I bought only works with 3/16" tubing, but it works so much better. Since it is also more compact, it is easier to do the flares from under the car, in tighter conditions. Leaking brake line fittings are not an area where anything less than a perfect double flare is "good enough".