Looks like the diesel fuel inlet metering valve (not a sensor).
http://www.dieselpartsdirect.co.uk/e...-valve-kit.htm
My 2011 TDCi has an oil leak showing in the same place.
I couldn't say with certainty where the oil came from
but decided it was from the fuel pump/cyl head joint.
I replace the gasket without using a sealant and it still leaks.
There is a fine line in the aluminium head casting which may be the cause.
Was advised to use an anaerobic Loktite gasket sealant next time.
Usual thing is to clean off and inspect, but it's very hard
with these engines in tight spaces. Maybe UV dye.