If it's an early HRO with the German silver dial (not painted black), do not destroy the dial. Replacements are almost impossible to find.
Also, never use emery cloth,sandpaper or other abrasive to clean those dials. I always preferred a cloth lightly oiled with WD-40, and lots of polishing using a soft cloth. Eventually the oxide will go away and some shine can be restored. Abrasives will permanently ruin the surface.
I once bought one of those receivers thru the Yellow Sheets. The receiver was in excellent condition, but the seller said that before shipping, the dial was a little corroded, so he "polished it up for me." He had sanded it with a fine grade emery cloth, and the dial calibration markings were partially and permanently eroded away. Reminds me of the time when I was about 7 years ago, and I got into my uncle's collection of Indian Head pennies. I used sandpaper to shine some of them up to a bright copper finish. No need to even mention his reaction.
National replaced the dial with the black painted version after the first year or two of production because the German silver tends to tarnish to a dull finish.
