BMW Repair: Random misfire, oil filler cap, vacuum leaks

Question
I own a 1998 540i (E39)just had it back from the dealer who replaced the cam sensor and O2 sensor, $640.00 and one week later I have another problem.  In an effort not to have to go back to the dealer I purchases a FCXII scan tool which says that I have random misfiring in the engine. It also specifically designated cylinders six and seven with random misfires.  I checked under the covers and noticed that my inner valve cover gaskets have leaked some oil on top of numbers six seven and eight spark plugs.  Thinking this was the problem I cleaned up the excess oil, replaced the spark plugs and checked 0hms on the coils.  This did not correct the problem. Any ideas will be appreciated.

Answer
Philip, Leaking valve covers can indeed cause misfires, I would replace them post haste. Mark the coil and swap them to different cylinders. Note the new locations and clear faults. Drive the car and see if the faults return to same location. Also check the PCV valve on the back plate of the intake manifold. With the engine idleing, turn the oil filler cap and crack it open just a little bit. If you have a huge amount of vacuum under the cap or if it makes a strange honking noise the Valve has failed. Also look for vacuum leaks around those cylinders by spraying brake cleaner down on the intake gaskets and around any manifold or throttle seals and listen for a change in RPM. That should give a few avenues to try.
-Evan