Cleaning Model M Keyboard

[Miller88]

I have a Model M 6-3-92. It's my favorite keyboard ... and as soon as I get more money, I plan on buying another one of these. I just bought a German Model M keyboard (unicomp, supposed to be brand new and produced in 2006).

Anyway, my '92 model M is somewhat yellowed. I've been over it with 91% rubbing alcohol, hot water (on a cloth of course) and I can't get it un-yellowed.

It's not really terrible yellow, but slightly yellow. The keys are white still ... if that matters at all.

I also have a question about the letters wearing. What can I do to stop the tops of the keys from turning shiney and smooth like keyboards do after a few months of use?