Bit the bullet and replaced the servo with a metal bodied rebuilt unit ($350). The coolant leak from the old plastic bodied servo has been eliminated. I can hear the servo park with ignition off.

Unable to get heat in any mode (including defrost). I read that the amplifier is often taken down by a bad servo. Could a bad amplifier prevent heat from coming on? I thought getting heat in defrost mode is the fail safe mode. The aux pump is OK and anyway that is only needed when idling. Blower works and air moves to different zones when different modes are selected. AC does not work because of a refrigerant leak (will deal with this later).

Could replacing the amp solve the no heat problem (even in defrost) or should I look somewwhere else and fix something else before condeming the amp as the cause of no heat?

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1972 450SL
1982 300D Turbo