[72SB]

Barke line fittings, used lines attaching to new MC/proportioning valve and elsewhere, can leak as the old side flare has been slightly altered in previous mating.

I use copper flare washer to deal with that and has stopped every leak when I was confronted with it. They come in all brake line sizes and can be purchased on Amazon for a few $

Cutting and reflaring lines also works if you have the tools and the hard line length to accommodate cutting some off