Hi All,
Wanted to share a similar issue with my 2013 A6 3.0 BiTDi because it took me months to resolve this annoying issue.
Had a very slow coolant loss which was visible on the front sump below the water pump. Changed the water pump, no joy. Installed the pump again, still no joy. Changed the o-ring on the water pump, still no joy.....read the above stories, decided to strip the upper block. As per the following photos, the V-block was flooded, which also dripped down the front of the engine onto the sump.
Replaced the coolant regulating value (059 121 737) shown in position 1 as it was evident coolant was leaking on the shaft seal.
Replaced the intermediate flange (059 121 506g) shown in position 2, as there was a small tear in the seal.
Given the fact this was the first time i've stripped my BiTDi engine, the entire job took about 8hrs....the hardness thing was stripping and installing the inlet manifold as it a bit of a pig.
Hope these photos gives other 3.0 owners resolution to this common fault.