Study this real well, 69 Plymouth manual. When that valve moves from a broken line, what does it cover up? It WILL move to SHUT off the port that's lost pressure.
99% of all line breaks are after that valve.
How does the fluid get between the separate, unconnected, pistons in the master cylinder? What keeps it there? Magic?
My wife said I was beating my head against a wall, I think she's right.