I've worked on alot of bmw's for several years. They all end up leaking past the spark plug seals and cause problems with the coil packs. Replace the valve cover gasket, spark plug gaskets, and grommets. Be careful with that valve cover as the m50 cover has this shitty paint that likes to flake off, try not to get it in the engine. If you have an m52 engine the cover is plastic and can be a bitch to get off sometimes and might crack. Good luck and make sure to clean oil residue off the coil pack boots.