WARNING!: plastic tends to age faster after being exposed to bleach. The whitening may only be temporary and lead to an even yellower console. Experiences may vary. Bleach your console at your own risk!
Here's a guide that I haven't gotten around to linking into my site yet-http://superpcenginegrafx.com/cleaning_a_pcengine.html
Drinking a beer with cigarette butts in it (accidentally), I'm that guy.