One thing I read about the downside of the synthetic oil is that it might have compatibility issues with plastic engines parts. Of course, I don't know the plastic material that my engine uses (Mazda3 2007, 2.0L I4). According to the factory manual, it uses a plastic oil strainer, and plastic cylinder head cover which I can see. Is this concern substantial? A Q/A on the M1 website did not provide answer as they stated they don't have the information.