Not sure if this is a casting line or if it is a crack. Tried looking for other peoples photos, but they are all of the side view and not the front of the transfercase where this one is.

 

Looks like a crack...
Does it leak oil?

 

I don't know if it was leaking or not. It was seen after draining the fluid. It did make a suction sound pulling in air when I took out the fill bolt.

 

Mine always does that too. The vent lets air out when the fluid heats up and expands, but doesn't pull air back in when the fluid cools and contracts. I would clean the area really well, and fill it up. Drive it, and see if it leaks...

 

Got an email back from TRE stating its a casting line.. That's a relief!