I seem to recall that when I did my FX-3, I used methylated spirits and malt whisky. I rubbed meths into the leatherette residue, and drank the whisky. (At least, I think I did it that way round.)
I used Mr Aki-Asahi's kit. Just excellent. The old stuff came away with about half an hour's work, and the new covers go on very easily and snugly.