Was able to get under the jeep today and open up the rear diff. Everything actually looked really good. Sealed it all back up with RTV and bought a new fill plug. Only odd thing was, it didn’t take as much gear oil as anticipated. There are shims on the rear axle to angle the pinion up towards frame, which I’m guessing moves the fill hole down and effectively lowers capacity on the diff. I’ll research this a little bit.

Changed the oil as well. The near black obsidian that came out tells me either the guy had been trying to sell it for a while and didn’t care or didn’t care. Next on the list is why it’s running so rich.