I also find it helps to grease the back side of the flare and inside the nut so they don't bind while tightening. A little grease on the threads doesn't hurt either, or one or two loops of teflon tape on the threads for lubrication only.
You may want to look at the inside flare of the fittings, over time the get distorted and won't seal no matter you do to the tubing.
Joe
