Okay, upon further inspection, I do believe that the it is the intake NOT the thermo housing that is leaking. That coupled with the presence of "sludge" in the expansion tank, confirms my fears that the LIM gasket need to be replaced.
I can see on both the front and the back of the engine, where the intake meets the heads is leaking for sure, on both banks.
I know there's a link for the replacement process on this board, so I'll try and find that. In the meantime, are there any pit falls, specialized tools, etc... that I might want to be aware of?