65 Valiant 4th or 5th master cylinder still leaking

I called Dorman, Bendix, and Cardone. They all say each fitting hole is 1/4 NPT. I even tried buying a different 1/4 NPT plug to see if it would seal better. The hole where the brake line goes I guess is flared but when I look inside it has the flow valve cup or whatever it is with all the holes in it. The one that's leaking is just a bare casting with no flares just like and empty chamber type fitting. I'm getting tired of swapping them out going under the dash back and forth.