The bandswitch is easy to get at and spray with contact cleaner. Spray briefly then rotate fully back and forth. Be careful with it, though. It's a slightly weak design.
The shaft in the center of the switch is merely dimpled to hold it in place. Soldering the shaft to the switch mounts at a few locations will help a lot. If there's any play, the switch contacts may not be fully meshed. Rotate it slowly back and forth and see if the just the shaft turns a bit before the switch begins to rotate. If you have play, there's a problem. For now when changing bands, you can wiggle it back and forth till it settles into the right spot.
A service manual is at nostalgia Air:
http://www.transoceanic.nostalgiaair.org/
-Ed