Calculator Woes: Dark Spots and Viscous Liquid on Screens.

[mfleming]

These do appear to be polarizing film failures as Jeff described. Exposure to heat can accelerate this natural decay process. Direct sunlight for example. Having a number of different displays fail in the same period suggests an environment problem where they are kept or stored.

I don't know about the Casios but the HPs can be opened and their displays replaced with donors. Quite a task though.