it seems that the general feeling here at MS is to use the genuine MB coolant when replacing, and not the generic prestone or others that you can get anywhere.

not 100% sure of ALL the reasons, but most likely due to the corrosive (sp?) properties and the types of materials the MB cooling systems are manufactured with.

im sure its not cheap, but it sure is frequently recommended here.

you can probably do a search here for info on "bleeding" the system after refilling.