I don't think that running a chemical analysis is really neccessary. It sounds like your coolant is in need of changing, that's all. Coolant doesn't last forever and I'm sure that MB has a recommended changing schedule. Coolant goes through breakdown and also absorbs the various metallic and other elements that are present in the cooling system as well as create calcium/mineral deposits based on the minerals present in the water you use when mixing it.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012