I have the exact same problem. The leak comes from the nipple that the short heater tube attaches to. It is a press fit into the manifold and they leak there as well. As time progresses polymer material does get brittle. Any time you have 2 non like materials that join together via glue or press fit there is a potential for a leak due to the differing rates of expansion. Mine started as a pinhole leak and is progressively getting worse as I heat cycle the engine. Mr Jones seems to have the best set of instructions out there so I am off to do the PI swap as well. Those plates are the only way to go IMHO.