It is low mounted (front mounted)
In fact, i'd say that join is the lowest point in the whole system, as it lifts slightly in the tanks either side to enter the Cooling Element itself.

Not sure if its Hot side or the Cool side, i really didn't follow the pipe work, BUT, the other side has a Aluminium section of tube with a sensor mounted in it. It is not leaking on that side.

EDIT: Found this



Image lifted from here:http://www.estore-central.com/bmw-pa...-Air-Duct-Agr/

No. 3 connection is where ours is leaking dark black oil (small amounts)