I've recently bought a Commodore 64 on eBay. It was everything than beautiful.
1. Disassembling
For cleaning all parts accurate, I suggest to disassemble the device.
2. Surface cleaning
It's amazing what I've achieved with the combination of isopropyl alcohol (http://amzn.to/2uHrfTL) and some pressure. For removing some remaining darker flaws I usualy take baking soda.
3. Brighting yellowed parts
For retrobrighting I prefer brushing some hydrogen peroxide (http://amzn.to/2tObwpv) on the relevant parts. After that I wrap those with transparent foil. Normally I would put them directly into the sun afterwards (for about 8 hours), but a classic light bulb or uv-light will also do the trick - but will may take longer.
