Not that I have any experience in removing stuck picture tube sockets, but I'd caution against using a metal screwdriver anywhere near glass.....especially if it has sharp edges. The stress that you can induce is pretty amazing and can cause big time problems (read: cracks=implosion)

*IF* you wish to use something as a prybar then you'd probably be safer with a plastic or soft wood implement.

As far as using WD40, just be sure to wash off the residue after, most of it will evaporate due to it's high content of solvents, but you can never be too sure of what funkiness it may cause electrically.

Anthony (not a fan of WD40)