thanks for your response . . . I'm told that the misfire, bad gas mileage and occasional sputtering are related to the faulty engine [wire] harness and that the leaking head gasket was just something they noticed when they were performing an oil change. My service advisor didn't really offer any explanation as to what happens as a result of a leaking gasket other than oil escapes from the cylinder heads (and that I should really consider replacing the gasket). Given that gasket replacement is covered by my Starmark warranty, I already approved the service, but am now wondering whether more problems are going to be created by the replacement (it's supposedly a complex job, requiring the removal of a lot of engine parts).