Hi Jonny,
haven’t used any chemicals, definitely hasn’t been out in the sun.
Actually ended up asking over on the korg forum, and the guy who answered , happened to him too, strangely enough another Australian. Wonder if it’s something to do with our humidity .

Basically was trying to scale down. Planning on selling our family size home and moving to something smaller, so may not have enough room for 3 keyboards. Haha.
Oh well.