I make all of my own steel lines with flared fittings. They key to making a flare that doesn't leak is 1) having a GOOD tool and 2) using a drop of oil on the flaring tool when you make the flare. Additionally, once you get it made it's also a good idea to put a softer wire wheel to it and clean up any burrs and smooth it out.

I struggled with leaky flares for a long time before I finally broke down and bought a good tool. The one I am using now is a Rigid brand tool. Never had an issue with it.

1950 4100 - unrestored and driven weekly for almost no reason at all.