Im guessing certain pieces ,components in the lines ,servos etc have radiator fluid requirements.The evil servo in my 79 mb wagon gave up the ghost after a flush ,plastic piece ,split up the side ,was able to retrieve a junkyard piece for $17 bucks ,awesome deal considering these run $750 bucks to $1400. Ive recently taken the piece apart ,it looks like a thin gasket in the piece and the fact that its made of plastic,like a distributor cap, doesnt help the design.Why OH wHY DID MERCEDES GET MIXED UP WITH AMERICAN PARTS.