I have a 2005 vauxhall signum 2.0 dti the other night i had the service light come on and the car went into a limp home mode, with revs really lowering. luckily i was within 10 feet of home so i free wheeled and have parked it up. i checked the engine and found the highest joint between the engine block and rocker cover was filled with a bead of oil. all parts lower in the engine have a coating of oil as well. i have only had the car 6 weeks and so to me the car has felt no different and it has not overheated. there is no milky residue in the oil or smell from the coolant.i have attached a pic with the pat which appears to have failed circled, the picture is taken from the front of the car looking into the engine bay focusing on the right hand side of the engine block

is it just a case of the gasket needs replacing and oil refilling? or does it sound more sinister?
also any tips of how to go about things are very welcome, thankyou for reading
aaron