Water pump seizure while ‘dry’?

The XJ12 needed a few jobs - chiefly a new radiator. For a variety of reasons it took a couple of years to complete that job, during which time the car has stood indoors with the cooling system about half drained (i.e. to the level of the rad leak). Coolant mix was pretty fresh.

Yesterday I started her up and a loud belt squeal showed the water pump pulley had seized. I eventually got it to move with heavy torque and completed a couple of turns but it’s far too stiff.

Isn’t the seal a ceramic disc lightly spring loaded against a ferrous collar? I assume some water has got into the bearing. Anyone had a pump fail on standing?