Al, you were right, and here is how I found out where the leak was.

The first thing I did was swap clear dome lids between the main pump and the twin that runs the deck jets. The pump continued to lose its prime within hours of being turned off, so I knew that there must be an air leak somewhere else. Next, I let the hose gently run over the equipment in various places, but I never saw any noticeable bubbling to lead me anywhere. Upon leaning in closely, like some kind of ease-dropping detective, a faint high-pitch sound was heard at the Jandy valve that controls water flow from the skimmers and main drain. We took the valve top off, inspected the o-ring, and discovered that it was cracked! Since the set-up is twin to the deck jets line, we moved the o-ring from that one over to the main pump, and it hasn't primed this nicely since the first year we opened the pool! I so appreciate the care and help on this forum. Thank you for teaching me along the years.

Shannon