Any issues of late with the flare tools like this? With my cheapo and the new Cornwell tool it seems to leave some unflared tubing at the split line. I am blaming the not quite to size tubing that is available nowadays.
Quick cleanup with a file on the nut side of the flare seems to fix it but it is annoying.
You tighten/loosen fitting several times, to seat it. You will notice nut turns a little more each time. I do that with every fitting. A little extra optional step is a dab of anti-sieze between nut and tube. Can thank me later.