After doing timing chain guides we had a hell of a leak right where you describe: turned out to be the crush washer on the tensioner. Hope you find out it's similar.

My car with no significant coolant leak but apparently a tiny one (add a cup every couple weeks) has sucked the upper hose flat just when a little low. I must have had some air in the system didn't do a very complete "burp" which I did recently and haven't seen the flat hose in a while

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)