How did you clean the switch stem? They look brand new after your cleaning. I have lots of old dirty switches that need to be cleaned.
I use PB1 and water.
And rinse many times.. 
After rinsing.. I clean them in the ultrasonic cleaner.
And I rinse again.
My wife said "Water is more expensive than switches" 

And one of korean kbder find new detergent.
It is very effective for removing dust.
No bubbles.. 
I sometimes use it when there is much dust in the switches.
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