Well... Not a cleaning problem. Actually a broken actuator inside the "CH1V" switch section, it was the internal actuator position that was unreliable, not intermittent contacts. So, it will be full replacement of the switch assembly. Fortunately I found one and have it coming.
I desoldered and removed the A14 "Hot Signal Switch" circuit board from the top of the switch module. Tedious work but doable with careful heat application and copious use of solder wick. The switch module itself will take more time...
As Roseanne Rosannadanna said, "it's always something..."
