Tip for the day:
The single most important thing to do when working with hydraulic fittings and fitting adapters is to check and verify the diameter and taper of the threads before assembly.
They crank these little metal pieces out by the thousands, on machinery that is not being manned, and the product is not being checked for quality control. The machine goes a little out of adjustment and they have a barrel full of little metal pieces that are under size on diameter and/or have no taper at all, and they don't even know the pieces are the wrong size.
And no amount of thread seal or Teflon tape in the world will stop it from leaking.
OK, I am going to go back to working on my brakes, now that I have a fresh batch of little brass and steel elbows and thread adapters. After disassembling everything to replace the bad pieces, I will put it together _again_. And this time I hope to have more brake fluid going into the calipers, and less of it going onto the pavement under the car.
(And I thought flaring the ends of the little pipes was going to be the challenging part...)