'88 300E climate control won't stay off.
 

I got this car recently with over 200K and "0" button for the climate control panel doesn't seem to stay fully in the off position all the time. While the button looks to be pressed in, I can be driving and the A/C comes on by itself so I press the button again and it goes off for only a few minutes to maybe an hour until it gets loose again and the A/C comes back on by itself. Are there parts of the button/switch that can be replaced without getting a whole new unit?

Not unless you find a used one to rob it from. Probably just easier to use the whole thing if you got it used though. The electronic controller like you have is not very fixable.