Quite frankly I am not sure shooting some contact spray in them is gonna fix your problem. Not saying it won’t, just expressing doubt. My concern is fed by the fact that these buttons are so enclosed these days, that there really isn’t too much chance of them getting so dirty they won’t function anymore (and certainly not a whole bunch of them). Faders are really the only exception as they have, due to the nature of the beast, a semi-open connection with the outside world.
By the sound of it, the unit belonged to someone who didn’t push buttons, but rather hammered them. And if you hammer a switch or button long enough, it’s innards can become weakened and even break. Often there are spring like mechanisms that make sure the button returns to it’s neutral setting after being pressed. And the actual bits that make the connection inside the button/switch have a shelf life too. That shelf life is severely shortened by overzealeous use, i.e. hammering.
It looks real good standing behind a controller dropping your finger from chin height or even above your head onto the buttons, but it doesn’t exactly qualify as good use policy.
Having said that, to get to the inside of the buttons you often have to take off the top plate or the bottom plate. Attempting to remove the rubber/plastic caps is often destructive if you don’t know the exact way they are attached. Shooting through the cracks is, imho, useless. The caps will be bigger than the actual switch, chances are big you’ll miss the switch completely and just randomly spreak contact spray around inside your unit (and the stuff smells!).
Greetinx.
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