It is what is in the first picture I am wondering about, the se ond photo is from farther back. Which as you stated is the bell housing connecting to the block. I am wondering about the cover or pan in the background off to the right hand side?
I found it to be a front differential carrier gasket which is leaking according to a GM part breakdown I found online. However I was unsure and was just inquiring with someone who may have some experience. If not I will head to GM and see what they have.