The brief
Oil spots had been showing up on the bay liner under the 530i, a burning smell would build after a motorway run, and the engine had developed a faint misfire under heavier load. The owner brought it in before oil reached the plug wells properly.
The valve cover sits over the camshafts and valvetrain at the top of the engine, sealed to the cylinder head by a gasket. When that gasket hardens with age it stops sealing along one edge, and oil weeps out: it spots the liner, it cooks off on a hot exhaust and smells, and worst of all it can track down into a spark-plug well and start to short the coil sitting in there, which is what brings on the misfire.
The diagnosis
Off the engine, the valve cover gasket had hardened and lost its sealing edge along the long side. Oil had been tracking down the head and was just starting to seep into one of the plug wells, which is what was producing the misfire under load.
The gasket on this cover is integrated, so you replace the cover as a unit rather than fishing a strip of rubber into a groove. So the job was a new cover, with the affected well cleaned and dried while everything was apart, before the leak did any real harm to the coil.
The work
The cover and the intake fittings over it came off, the head face was cleaned back to clean bare metal, and a new BMW-spec valve cover with its fresh integrated seals and new bolts went on, torqued in the proper crossing pattern. The plug well that had started catching oil was cleaned and dried, the coil checked, and the bay reassembled.
The engine was run and checked for a clean idle and no misfire under load before the car went back to the owner.
The outcome
Dry head, clean plug wells, no burning smell after a road test, and the misfire gone.
The 530i went home with the top end sealed properly. For the owner that is the end of the smell and the stumble under load, and dealing with it before oil filled a plug well meant the coil was saved, a clean rather than a replace.