Hi everone,
My dad just got a '95 S600 this past weekend. The records indicate that the oil was changed this past september and has 10/30 weight oil in it. I've heard that the S600 likes a heavier 10/40 or 10/50 weight. Which is the best to use?

Thanks

P.S. This may sound dumb, but does anyone know if it has a 4 or 5 speed transmission?