[Richard]

Thanks for the clarifying info.

Then the heater core is likely your culprit. Open your generator bay and inspect the ceiling. White paper towels are your friend in this case for finding coolant leaks. The core is directly above the gen bay, and since water/coolant generally obeys the laws of gravity then what you reported makes sense. Yours would not be the first core to fail.

Here comes the good news/bad news. You can keep those valves shut and still use the coach. Obviously you will lose dash heat AND the engine coolant circulation through the AH. If you can figure out which loop is for the AH you could open those. If I knew which valve was which I would say. The bad news is I think replacing the heater core is going to be a CHORE. I would try to get some advice from Newell.