Noticed lately that my 04 350Z consumes ca 1lt oil per 1500km. At the same time and during a spark plug change I noticed oil on 2 of the spark plugs. The serviceman told me that it is surely problem with the gaskets and it has to be fixed by lifting the upper part of the engine to replace the gaskets. Is it so or can there be other reasons for the oil consumption and the oil on the spark plugs?