Doug,
I know you are a fully qualified Tiffin tech. My problem here is that there is no local Tiffin dealer in which I have confidence.
This problem, I would consider as being generic. There is one non-Tiffin dealer I can go to if I can't work this out myself, but his techs stay overwhelmed. The biggest obstacle, at my age, is getting where I need to get to access the problem.
At the age of my motorhome, even though the engine, interior, and major components are still in generally good shape these types of aggravations seem to come one after another. Connections age and corrode, hoses get brittle and electronic components don't last forever when left to the elements.