When I rebuilt my calipers, I put new lines on them, they leaked like a sieve. Pulled the lines off, looked down into the threaded holes in the calipers the lines screwed into, and saw that there's a brass doo-hickey at the bottom of each hole that the lines are supposed to seal against. Mine were buggered up. Calipers been rebuilt too many times, maybe. Anyway, I could not find a source for the doo-hickeys, and so ended up just buying a set of rebuilt calipers. I still have the ones I rebuilt, in case I ever find a source for the brass thingys (must be a name for them, but have no idea what it would be).