leaking brake valve

Is this the same valve? late model A-body disc/drum with built in rear hold of valve?

The nut on the top for the front brake line input from the master cylinder (Rear Port).

It just uses a copper washer for sealing to the valve body. Are you sure its tight or is the fluid actually coming from the line fitting connecting to it?

Did you get stainless lines??? If so I understand you have to put bit more beef on them to get them to seal.