So yes, the transfer case. When I took it out of the car, it was black, which I presumed was like how cast iron skillets are black, since the outer case was probably made of cast iron. Turns out it was that color because that’s what you get when you mix burned, leaking transmission fluid with the accumulated layers of dirt from off-road hi-jinks. Its original finish is mostly visible now.
It might seem like I’m complaining a lot about how dirty everything under this car was, but if you could see it in person, you’d be just as sincerely baffled as I am at not only the quantity, but the sheer tenacity of such grime. It takes serious stuff to get down to the actual metal on these parts. For me, it’s as Ron Burgundy would say: I’m not mad – I’m impressed.
Circling back to the transfer case itself… It was stuck in 2WD and I thought there was some internal failure that was responsible for this. The good news is that the internals all seem fine, so I shouldn’t have to take it apart. Once I got the adapter housing off, the vacuum-operated actuator that sits on the outside of the transfer case, and shifts the thing between 2WD and 4WD, wasn’t bolted in place anymore, and I could shift it manually. When I do so, everything seems to operate normally. It’s the plunger in the actuator itself that won’t move.