Found the leak. Just close to the water pump in a rubber seal.
Edit: Image doesn't want to show up inline, use this link instead:
https://www.dropbox.com/s/uegjmxpv6r4zvvv/2015-08-06%2020.39.36.jpgIf I would speculate in why this happened then my best guess is that the one who fitted this rubber hose used to much force when clamping it down. This should not happen on a 3 year old rubber house with such a low mileage engine.
Does anyone know where I could obtain replacement instructions? Spare part number? And also instructions on how to flush the whole cooling system.