I found the leak. Very small and didn't cause the problem on it's
own. It did however, cause the water tank to draw down faster than I
expected. It must have been just on the verge of sucking air when I
when I went to sleep. Now I know where that little wet trickle I
thought was collected condensation was coming from.

Next on my to do list, a way to check the fresh water tank level more
easily.

The pump is dry as a bone around the diaphragm, even after pumping
enough to fill the holding tank 3/4 full with fresh water to flush it.
The sink drain "T" into the head intake line works great although it
means a lot of head pumping.

The leak is in a metal to metal joint at the cold water inlet to the
heater. The drip runs down the hose to a low spot so it isn't easy to
spot.

--

Roger Long