I’m not sure if the micro switch is the only sensor, but I generally agree there has to be a finite number of possibilities. For instance there’s a neutral position sensor on the transmission which will prevent the ECU from allowing you to go into 4Lo. But it could also be a bad solder joint on the ECU - or even a bug in the ECU firmware itself. FWIW I don’t think it’s actually a fluid or grease-hardening issue because the failure is nearly instantaneous on startup and it’s not because I’m pushing the CDL button - though I sometimes can recreate it when cold if I push the button....Unless there's a switch or sensor in the transfer case that I'm not aware of, it has to be associated with the microswitch, or the solder joints shown in the video above...