[sdiy] rotary encoder failure mechanism

[Dave Manley]

When an encoder becomes unreliable is it because

1. the switches are worn out
2. the switches are contaminated and need cleaning
3. the mechanical cam that operates the switches is worn out
4. debris from wear on the cam/switches is blocking the switch operation
5. ???
6. any and/or all of the above?

Anybody take one of these apart and do an analysis?  Does spraying 
cleaner into an encoder really do anything?

-Dave