48g over-zealous cleaning

[Allen]

I've had good luck with "slightly damp" long-pile wash rag or towel.
Lay it on a flat surface and turn the calculator face down and gently rub the calculator on the towel in a circular motion.

From time to time I need a Q-tip (TM) or similar cotton swap with only a little water or diluted alcohol to clean in between the keys. But this should be done with care, as the OP suggests!!