Good call, Harry. I had a plumber out today. He said the tank is
definitely waterlogged (fortunately for me the tank is still under
warranty). More disturbing, however, is that pressure is lost even
when the water to the house is shut off. As you surmised, there's a
leak somewhere between the well-pump and my basement where the tank is
located. I have no check valve in the basement and this probably
allowed me to notice the loss of pressure when the house water supply
is shut off.
Any thoughts on what I can expect in the way of finding the leak?