60DRB

From what I read on these sites, the shift motor is more likely to malfunction and/or seize up when it is little used. More frequent use keeps the parts working better. Mine's a manual shifter though, so I don't have personal experience...

thump

I would agree with this. It's been my experience that with a 4WD vehicle you actually need to use 4WD every once in a while or you'll start having strange problems. Things need to stay lubed.

Once you can get it into 4WD again, try putting some miles on it.