Please don't use motor oil, WD-40, Armorall, wax, etc. Those are temporary
coatings which must be reapplied and actually attract dirt over time.

Use Novus Plastic Polish #2 and a soft toothbrush, followed by brisk rubbing
with a soft rag. The shine will last forever.

Available from many online suppliers, such as Antique Electronic Supply,
http://www.tubesandmore.com/ .

I have used #2 to polish hundreds of radio dials, knobs, bezels, etc.

Don't use #3 -- too abrasive for most situations. I also don't have much use
for #1, which is more of a protectant for something that's already shiny
(and could be cleaned up just as well with mild soapy water or Windex).

If you clean and polish the knobs correctly, there is no reason to spray
them with any sort of new coating. The knobs were not sprayed with stuff
when the radio left the factory.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html