I'll throw in my twocents I can't find where the original poster said he was using stainless or steel lines. The corrective action is the same regardless. If the fittings are leaking, unless the machining on the fittings is poor, the tubing flare is defective in some way. Otherwise the fitting wouldn't be leaking. I have a selection of stainless steel female fittings and with a GOOD tubing wrench and lubrication on the nut, I tighten the bejesus out of them. This re-forms the flare on the tubing so it will seal. Never failed me yet. As a note, I've only used stainless lines one time (brakes) and never again. I had to tighten them so tight to stop them from leaking I was afraid I would either strip the fitting or gall it. Again, just my twocents, feel free to do whatever turns your individual crank.

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".