I noticed from reading posts that with a new engine and the desire to use a fully synthetic oil that one should FIRST use a petroleum based oil for the first 5000 miles or so before switching to the Syn! However, new vettes come with Mobile 1 Syn from the factory and GM states that this completely satisfactory. Thoughts? I asked GM about this concern and they told me that first using a petroleum based oil is all bunk! Not needed!