Problem Switch...
A loose shaft coupler  allowed the rear shaft to slide free from the forward knob and shaft. You can see the locaton of the shaft coupler. It sits right in front of the first contact waffer. 
The problem... the mode switch has two shafts, coupled between the front detent (1/4 inch shaft) and te rear contacts (3/16 flat walled shaft). The coupler is plasic and this one had become loose; not gripping the contact shaft as it should.
This allowed the rear shaft to slide back with use until it was clear of the coupler.  I had a couple of choices here to fix this. I could have taken the switch apart and used epoxy to glue the shaft into the coupler. I decided against this approach because the coupler was so close to the contacts... any epoxy on the contacts would ruin the switch. Another reason is that once glued together, the switch could never be disassembled again. Also, the switch can be inserted 180 degrees off, and making that correct orientation during assembly was a risk I did not want to take..
Instead, I chose to make a retainer for the back of the shaft, out of Styrene plastic. I used heavy walled plastic pipe and a small section of sheet plastic. This was assembled to make a cap, which was worked  to the precise length to just clear the saft. This was glued to the plastic shaft support at the rear of the switch. This keeps the shaft where it should be and the switch is still serviceable should the need arrise... 
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