To my knowledge you are not supposed to use Platinums in a Mercedes. As for leaning out the mixture I don't know, but it may be the same as the 4.5. If it is then you can just turn the screw on the MAP sensor. You will find directions/pictures for this in many recent threads. If you do have this, turn the screw a quarter turn or maybe a little more clockwise. Here is a picture of the MAP.
Tim
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