Although it may be a PITA to actually pull a few coils, it would let you know if there is oil or water is the spark plug well. This can cause problems. Did you guys just have some really, really hard rain about a week ago?
I do not know this is your problem, but something to consider??
Xoutpost.com - powered by BMW X-sav Enthusiasts!
If you search around, you will see this can be a problem with the E70 and the 6 cylinder engines.