“…. As I said before, there is no way under normal circumstances that the ports for each brake circuit inside the warning valve can be blocked by the moving parts that are inside…”

If, by design, that shuttle valve WERE to close off the leaking circuit then it would, in effect, dead head that circuit about 6 inches from the master cylinder. That blockage would prohibit the driver from being able to apply much brake pedal pressure to EITHER circuit, even the good circuit. That means little or no braking. It’s hard for me to believe the switch block would be designed that way.