Thank you, sir. Exactly right.

OK, the two flange connector goes straight into the heads thru the lower manifold, as I thought I remembered. The water pipe under the lower mani goes straight to the water pump, IIRC to the pressure side of the pump, but that may be wrongo. I doubt either path is blocked in the metal. This leaves a blocked hose, perhaps from an internal collapse. Replace the hoses.

Not responsible for advice not taken...