What is this hole??

[Mchambers]

F25886B7-E94A-43C8-8113-AB86D7F0AD01.jpgDF76D018-4C6F-4308-8B73-7A8CEB347EE2.jpgJust got a 56 CJ3B and have been playing with it the last few weekends. Just noticed some oil und6F78BE2B-5D1D-4008-ABF4-BED7CC498094.jpgerneath so crawled under to take a look. At first I assumed it was brake fluid because I had taken off the cap to check fluid and pushed the pedal and some shot out. However this looked black so that’s what got me looking. I found a hole at the base of what I would normally call the bell housing. It’s a small hole...measured slightly smaller than 7/16 and there doesn’t appear to be any threads. However, I can look in it and see what I think is a gear tooth. There is a large drain plug nearby that I assume is for the transfer case or transmission. Besides that drain plug and the drain plug for the oil I don’t see any other plugs. I found a diagram that looks like this could be for the transfer case but it’s just much smaller than most drain plugs. I’m attaching pics. If anyone has any advice I’d certainly appreciate it. Sorry for the messed up pic!