Managed to get it out this afternoon.
Needed to drill a bit into the screw head with a 1mm drill bit. That screw is made from some quality metal, let me tell you. Broke the first bit, and then inflicted a tiny scratch next to the screw, despite my protective measures. The drilling hardly seemed to make a difference, but it was enough to get a bigger screwdriver to get purchase. A not insignificant amount of pressure finally saw it move, and the rest was easy.
RAM out and in, 10 minutes max. Fired it up - and all good. Will pop in to the various iStores and Digicape and check if they have a spare screw the next time I am in town.
Thanks for all the suggestions.