I have taken over maintenance on a 2007 Mercury Milan. It has some warranty coverage left so I would like to stick to approved oils. The manual states WSS-M2C930-A oils are to be used. There are several oils that meet this approval, but is there a way to know of this approval has been superseded or replaced? Some oils are WSS-M2C930-A and some are WSS-M2C946-A. What is the difference? This is my first voyage into Ford approvals.