Front and rear diffs taken care of. 61k miles of RTV collecting grime was not easy to scrape off. Went with Lube Lockers on both and didn't have any leaking after a 15 minutes test drive.
No damage or worn/sharp teeth. Just that stanky gear oil smell. Spray painted the diff covers black as well. They look good, but don't exactly match with the rest of my rust-colored underbody.
I'll definitely be maintaining everything better from now on though. Thanks again to everyone for all the knowledge and info.