Well, after almost 96,000 miles it was time for a new water pump. After replacing the inferior original thermostat with an upgraded one in 2009, I once again started noticing coolant loss from the reservoir tank and hearing the familiar sloshing sound behind the air conditioning/heater controls. The sloshing sound was coming from the heater core indicating that the coolant level had dropped and air had been introduced into the system. I figured it was highly unlikely that the thermostat gasket had failed again. A quick peak under the car during an oil change revealed that quite a few blue coolant boogers had dried on the A/C compressor, which is directly below the water pump. Time for some wrenching.