Look for coolant puddled in a small indentation just under the water pump. Just having replaced mine, I would imagine that is the cause of your loss of coolant. The job cost me nearly $700 with a new serpentine belt for good measure at my neighborhood indy. That and they did not R&R the thermostat and refilled the radiator with green coolant. I am p.o.'d about the coolant. Have ordered and received a new thermostat. Plan to take it to the indy and have them flush and refill with MB coolant at no charge and also swap out the old thermostat for good measure. You might want to be specific about what you want done if you pay somebody. I hear the DIY is a major PITA. Shop time is six hours.