In theory (!) heating it red hot, then doing the 2nd flare should be better.
Annealing copper works. I've done it (not necessarily for a double flare). But I'm with you on using a compression fitting instead of a flare. Much more dependable.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.