I was sick and tired of looking at a nasty looking Amiga with yellow all over it. I said what the hell and tried somthing new.
Get a bottle of Soft Scrub with Bleach. Get a Dish Scrub Brush. Apply it all over the plastic and rub it like hell. I had to run the brush under the hot water to thin the soft scrub out a bit but it got the thing looking beautiful.....dare I say it almost looked brand new. Give it a try.