[Ron Ramirez]

The stuff on the cap.....it seems greasy, not dusty. And it is on one side of the cap. If it is cadmium-based, where did it come from and why is it there?

This is what happens to cadmium plating when it deteriorates over the years. I think it usually occurs as a result of the radio being stored someplace like a barn or basement.

For the sake of your health, put on a respirator and gloves, get some suitable cleaner for metal and get that stuff off your tuning condenser! (And do this outdoors!)