Installed the O2 sensor and that has cleared up the check engine light. After reading up on the task online, I figured I was in for a fight, but the whole thing didn’t take long at all. I bought the Bosch replacement unit, I’ve had good luck with Bosch kit in the past. It even came with anti-seize already on the threads.

Next up is the leak from the transmission/transfer-case area. Considering that the fluid smells more of gear oil, which is found in the transmission, than automatic transmission fluid (ATF), which is found in the transfer case, I’m going to say its the rear output shaft seal on the transmission. While the part(s) are not expensive, it’s a bit of a job to get to it. The skid plate will need to be dropped, but that’s holding up the transmission and t/c so care needs to be taken there. Then decouple the rear and the front driveshafts, then separate the t/c from the transmission. Then you can change the seal. I’ll probably replace whatever seal I can while I’ve got everything apart. Plus a fluid change for both, to get to a known good baseline. Thankfully, it looks like the original bolts have been replaced with new bolts (probably when the lift was put on) and I’m hoping whoever put in the new bolts put on some anti-seize to make future removal easier.