One problem related to engine head gasket leaking has been reported for the 2007 BMW 3 Series. The most recently reported issues are listed below.
Burning smell in cabin. Changed cabin air filter without any improvement. Dealer. Oil from valve cover gasket leakage is an issue in this model. Did internet research. Apparently not uncommon at all to have this problem. This is a health hazard-smoke inhalation and also a fire hazard. I contacted BMW corporate office and was told this can happen. No further information given.