From Danamania's web site, i found some helpfull tips (I don't know if they apply to Amigas as well ;-) ).
What a little time and a lot of bleach can do. I pulled the case apart and soaked all the plastic parts (keys included) in chlorine bleach for a few hours. After a rinse and a hand-drying, it all came up much nicer looking 
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VOYEUR UPSKIRT
