I would’ve got it fixed sooner 
, but I had another project on the workbench last evening after the postman brought me a small package from China 
I got lucky in guessing what my poor abused GTM needed, just a new switch. The first one turned out to be all I needed when they arrived, a SP DT switch like these:
No Handle Ultra Mini Micro Switch SPDT Sub Miniature Micro Switch
I had to do some more fiddling with the RF shield, with it finally coming completely off before getting reliable operation. I think the big crush pushed something to where it shorted, so I had to lift the loosened shield with some toothpicks, then just took it off as the simple solution. The shield likely is necessary in some high RF environments, but I think it should work OK unshielded. I haven’t tried pairing it yet, but hope it will replace a intact GTM I use as a home node. With the switch on the extension wires already, I can locate it outside the watertight box making it easy to reboot. Will do some testing on it to confirm proper operation soon.