Oil leak from Cecil!

[benfj180]

Hi guys,
Looking for a bit of advice re. leak. Couple of days ago I noticed a few drops no more the size than approx 4 no. 2p piece sized drips of oil (before you ask, yes defo oil, I checked, not trans fluid).
With the car on the ground could not see an awful lot other than the sump plug cover looking damp.
Got the car onto a family members ramp and started to investigate. The oil seems to be coming from the top of the engine, and in the most inconvenient place the back! A sensor, when looking the in the engine bay, just left of the rocker cover looks damp and potentially the seal between the rocker cover also looked a tad damp?
Are these places to start investigating and are they a nightmare job to do? What sensor is it? My oil level is still max after 3k miles of ownership so she is certainly not going dry.
Any advice is appreciated, cheers