Unless you live where it gets cold, cold, then I would not use any oil in a M-B with less than a 40w upper rating (40W upper viscosity with a 0 or 10 lower rating, a 0 rating will work quite well anywhere below the sub-Artic winters of northern Canada for example). Don't use any oil additives that would cause the viscosity rating to be lowered (i.e. Techron, Sea Foam, ect.). It is not the case of dirty components but, simple, the action of metal being chilled causing contraction and widening of valve lifter clearances because of this "contraction action" (sometimes I just love the Yinglish language). And, when the spring thaw comes, the valves will behave themselves and hush their clattering.