Here is a copy of a message I sent directly to Kevin.

A couple years ago W8FIX told me that a heat gun will take that white off the keys. I just tried it before recommending it to you, and it works like magic. It seems to turn it into a liquid. I then wiped the keys with a paper towel and alcohol but the paper towel only took off some brown. The keys may have been very dirty besides being white.

I used Harbor Freight's least expensive heat gun. It is also great on heat shrink tubing.

Even with the heat gun eight or more inches from the keys, it worked well

I hope this might help somebody.

Tom   N3CRK