jason, the manual is a fossil. oils have advanced, there are synthetic 30 or even 20 weight oils that will outperform the 40 and 50 weight oils of the time the w140 was produced and meet SM/SL/SJ/SH/SG/CF. i'm not saying you should use a 30 weight oil, if you have had great results with 40 weight oil than stick with it, but don't come to conclusions that 30 weight will cause engine damage. thinner oil will flow better at cold mornings, and most of engine wear comes from cold starts. anyways the engines are the last thing to fall apart in these cars, so oil grade/brand won't make that big of a difference since most of w140 don't take their cars to the track.The manual says 15w40, or even 20w50 for most climates that don't see freezing temps.