Now, I am even more confused when I look at this picture. Is there a guide for its removal?

 

Found this video of the whole process: At 9:00 the guy actually shows where this housing is.

 

that is the thermostat housing, and the block under it needs to be removed, should be 3 bolts

 

Why is this thread in the GM Recall Campaign section ?

FYI. This thread started out asking where the leak could be coming from. The water pump was suggested. Never did see anything posted where it was confirmed that's what is leaking.
I hope you're not just replacing the water pump hoping that's the problem.
( maybe it's not the water pump. The O ring on the coolant tube or the tube itself ? )

 

Looks like water pump. It is definitely not leaking from the tube. I checked out the other side.

 

Moved, thanks FMG!

 

I guess you could look at the link I provided to the water pump replacement how-to. It skims past the tube and housing removal because it is intuitive. I.E.: remove the bolts holding it. The only "magic" involved is the gear holder the rest is "remove & replace".
What is confusing about the picture? My intent was to show the transfer tube from the t-stat housing to the pump. It has O-rings on the ends; I suspect they are your leak.