[Elecraft] K3: M3 key issue

[Philip L. Graitcer]

I purchased K3 #696 from an estate. It works fine, even after I did  
the mods, except the M3 and M4 memory buttons need to be pushed hard,  
rather than tapped. (As we say in the South, this button needs to be  
mashed!). They work, but it's not a simple tap, so they are not  
convenient to use.

Is there a simple remedy to clean up these contacts?

Thanks,
Phil, W3HZZ