[Tubesforme]

...yesterday I removed the pushbutton assembly and it's filthy.  What's the best way to clean this up?

I have cleaned several switch and coil assemblies. First I used a small brush and canned air. then I used DeoxIT D5, but used only a very small amount and followed that using foam cleaning (like Q-tips) tips, from the local CVS store to carefully wipe all of the contacts. You already discovered the final step and that is to carefully check all connections for bad solder joints. I have never had any problems using this technique.