As audio equipment ages all contact surfaces, that is switches and connectors, become oxidized and can develop a minutely thin coating of plain old dirt (airborne contaminates like tobacco smoke, other kinds of smoke, soot, smog and super-fine dust). This condition can render a piece of equipment intermittent of unusable. This can be very aggravating, especially if the unit is otherwise valuable or just valuable to you. There are many sprays on the market that claim to clean up dirty and oxidized switch contacts. Some of these work on very lightly oxidized and dirty contacts, but they are useless in many cases. The cleaning effect of many sprays is very temporary as well, often lasting only a few weeks.
The reason that most sprays don't work is that they can't really scrub off the dirt and oxidation. All they do is rinse away whatever is loose, dissolve a very small amount of oxidation and in some cases leave behind a lubricant. The lubricant hides the fact that most of the dirt and oxidation has not been removed. As time goes on, in a few weeks or months, the switch is grungy again because the lube has dried up. Also, because only a small amount of the upper layer of the oxidation was removed it grows back rather quickly. Yes, I meant grows, but not like a plant, it grows like a rust, because that's exactly what it is.
At World Pro Audio we use a secret blend of safe chemicals and polishes that literally polish away the dirt and oxidation. Our technique removes upper and lower layers of oxidation so it doesn't grow back right away. Nothing else works as well or lasts as long. In fact, in 15 years no customer has requested a reclean!