I would NEVER run 30 weight oil. Look, screw the manuals, any of these 0w40-15w50 oils is fine, unless you are in Canada or something (and then 0w40 is probably the best choice). There is an Indie shop here that runs 15w50 year round (NC climate). They have been in business 20 years, and you will see anything from a 50s Cabriolet to new models there. The guy knows his MBs. He says the extra protection from 50 weight oil might cost you 2mpg, but it is worth it from a wear standpoint.