Rover owners: Rocker Cover Gasket or...

Looking at the car today (2003 Streetwise 1.4) and noticed there is some oil on the engine block. The coolant is a bit low but otherwise looks ok (I think), and there is no buildup under the oil cap. Not sure how long it has been like this. Can't have been leaking much though, I have never noticed any under the car.

Having searched a bit it seems this might be a 'rocker cover gasket' problem? Or is it something more serious?

Thanks