I am going to change engine and drive oil this weekend and would like to switch to synthetic.The manual recommends the same oil for the engine and the drive;10w/40.I haven't seen 10/40 but am considering Mobil 1 15W/50 for both.Does mobil make a synthetic 30 wheight I could put in the drive?Iv'e searched previous threads but it only confused me.Whats a good way to go?Thanks to all who care to reply to yet another oil question.