FINALLY!!!

After searching and searching I finally found the solution...

the 2007 E70 does not have an electric water pump. The procedure that everyone keeps telling me to do is not correct for this one year

Why BMW decided to do one year of the E70 without an electric pump is beyond me but that's the case. I found a post on BimmerFest with a guy that was having the exact same issue.

All I had to do was fill the expansion tank. start the car, leave the expansion tank cap off and let it run for about 15 minutes with the heater on full blast and keeping an eye on the coolant level. drive it around a bit and then re-check the level. DONE!

What still boggles my mind is what caused the leak in the first place... because this is EXACTLY WHAT I DID when i originally attempted this job yesterday. And suddenly, the coolant sensor is leaking like a siv...

Looking at the old expansion tank and temp sensor (that I just replaced with a new one) reveals that the temp sensor O-ring is GONE... like not there at all... POOF! So again, I have no idea what caused that but now the problem seems to be fixed.