Weird hole in SM465?

[Texas]

Please forgive my ignorance, but I was under my ‘89 K2500 this afternoon replacing the oil cooler lines and I noticed the hole you see in this pic. It’s near the PTO plate (that I installed when I removed the PTO). From the PTO plate, it’s towards the front of the truck. Is this part of the transmission? How big of a problem is it? Any idea what the heck could’ve caused it?
Thanks for your help.

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[Texas]

Ok, so I think this is the bell housing (sorry, I'm learning!), and based on the photo in this thread, the hole looks like it's supposed to be there https://www.gmsquarebody.com/threads/sm465-bellhousings.8446/ Can anyone confirm? Thanks.

 

[Nad_Yvalhosert]

Looks to be a drain hole in case of oil leak or water submersion.
Pretty sure the Getrag junk on my '89 has one. I'll confirm ASAP

 

[MIHELA]

Yes it's a drain hole. The NV3500 does also have one. It's so water or fluid leaks have somewhere to go other that the clutch housing.