I have lapped/burnished mating surfaces when they fail to seal properly. Always "double wrench" fittings, after joining all connections finger tight while "wiggling" them to settle. And, yes, keep checking the initial positioning for being "square" on both connections and bend as required to get them square. "Forcing/pulling" an assembly together rather than working it into proper alignment will almost always result in a leak and frustration. Almost everything involving mechanical assembly requires patience and assurance of proper procedures, or you will just keep expanding your vocabulary and throwing 10mm sockets into the void...
X2, I feel confident of a good seal when I can turn the nut finger snug on a line and not using a wrench to wind it home
That worked great for me on the steel fuel line I bought, after leaking at the fuel pump the first time around.
I ordered a SS fuel line from In-line Tube for my ‘68. Spent all afternoon trying to get it to “not drip”. Finally gave up, twisted it in a knot and threw it in the trash. Ordered a regular steel fuel line from a different company and it worked perfectly on the the first try, no drips, no leaks.
I’ve always shied away from stainless lines for our cars, plain steel will outlast us as much as we drive ‘em and the conditions we drive ‘em in. Now stainless brake and fuel lines for daily drivers, THAT makes sense