Ya it is attributed to a 59 cent o-ring. It's not rated for the correct temp and ends up shrinking and becoming brittle. I came out to my car one day after work and it looked like I drained the coolant on the ground. The puddle was huge.If I remember correctly it was on the right side of the car (under engine bay).
Is a tstat leak common?
Problem is if you mix different color anti-freezes together sometimes they turn black. I know you aren't supposed to mix colors but some people can't read. lolmight sound stupid, but taste the fluid, if its bitter/sweet to the taste and you regret doing it, and cringe a little like, eww thats nasty, its coolant, but if its oil, you'll see that your finger has changed a different color, so no reccomendations on tasting if it looks like oil. 
You know that caught my eye too but I was't going to say anything....Moved to "Ford Focus Technical Chat"
BTW, I do have one question...
Is that a welded aluminum plate on the bell housing?
^^^Directly underneath your thermostat housing in the 3rd picture.
If so, the previous owner may have had an encounter with an exploding flywheel. [eek]