neil is right - when you do use a damp cloth though ....
switch off the screen and give it a minute or two (the heat from the psu will evaporate the "damp" and just make the dried on gob even harder
lightly wipe wait a couple of seconds - then rub off
if you must use fairy .... dilute 1 drop in a full sink of water....
(natural soap is best (same dilution) - stardrops ... or anything you can use to handwash wool)
AND DON'T PUT ANY ELBOW GREASE IN IT at all
the membrane and support panels are very thin - it doesn't take much