Dark Buildup around that appears to be oil leak - Pictures

[gorilla p]

I have a 2007 Aveo5 LS. I have a dark buildup that appears to be a leak of some sort. It is just sbove the aluminum wall is that says "Stop - Hot". It appears to be just under the oil crankcase. On the bottom pictures, you can see where it is in conjunction to my dipstick.

I am curious as to what kind of leak would cause this. I'm also curious as to what would cause this kind of leak.
I can provide more pictures if it will help.
I am also still covered under the 2 yr- 24K mile maintenance warranty as well as the 5yr 100K mile powertrain warranty. including

• Valve covers
• Oil pan, seals
• Gaskets

I assume this would fall under one of the above categories?
e.