I have heater problems with my 95 E320. It makes some noises, acts unpredictably. I checked the aux pump and the amp draw seems to be ok (960 milliamps). When doing that, I noticed that the whole pump/valve assembly was very hot, and the valve was slapping on and off, sending surges through the coolant loop. Is this symptomatic of the pump needing to be replaced, the push button unit bad, or something else?