I'll try to respond to everything LOL
Yes, the boat was properly winterized for winter with antifreeze
in the fresh water lines, including the pump.
And yes, we are talking about 2 seemingly separate issues, but I too suspect they are somehow related.
I have not yet tightened clamps on the hoses except the intake and outflow of the pump. When I feel (with bare fingers) around all of the connections, there is no water. Anglefish can't feel water either - and I should note that the leak (puddled water) is confined to only the locker where the pump and distribution headers (both cold and hot) are located.
The pump does not run dry, and immediately after turning the water on, the flow is good but quickly dies off to a dribble - thus we're dealing with a blockage somewhere. And because it affects both cold and hot, the blockage is somewhere in or before the cold water distribution header (that feeds the water heater.) No? Oh, and the pump is a centrifugal pump, not piston. I'm saving the piston pump I took out for rebuild
and repurpose. LOL
I think I've answered everything. THANKS AGAIN for all the comments, everyone!