Forgive me for this query.

I have noticed that just under the plastic engine cover at the front of the engine, between the oil dipstick and the oil filler cap there is a valve of some sort with a switch on it. There seems to be a light coloured pipe connected and I see that there seems to be a seepeage of oil around this valve. From this pathetic explanation can someone advise me of what I am looking at and answer the question why would there be oil seeping. The car was in for its 30,000 mile service and there was nothing reported. Thanks