Crack/chip by rear main seal?

Found this today when draining the front diff. Is this the bellhousing? Seems like a chip.. but certainly in a weird spot for road debris to hit. Thoughts? Should I be worried? Truck drives/shifts perfectly. No signs of leak. Truck has 40k.

I can put my car key fully inside.

 

Not a crack, it is intentionally cast with that small opening. It acts a a drain and will also be a tell-tale of rear main seal leak.

 

This right here

 

Thanks gents

 

the most perfect crack/chip i have ever seen......its drain hole no doubt

 

Weep hole. If oil comes out of that hole, it's telling you the rear main is leaking.

Also you can stick a borescope to inspect the rear main through that hole.