Phil wrote ...
Pretty common leak - will need resealing. Usually with Silicone sealant.

Catch it sooner rather than later though as it'll be dripping onto the alternator (as seen) and will end in alternator failure.

The unit houses the air inlet temperature sensor, inlet air pressure sensor and a couple of other devices, which can shut off the air from the turbo going through the air cooler when the charge air is still cool. It also houses a heater which heat the cool air to the optimum temperature.

It's all down to emmisions really.

[shadowbox=http://c4owners.org/images/c4/dozer2.jpg|:: Air Doseur||]http://c4owners.org/images/c4/dozer2s.jpg[/shadowbox]