A small addition to this thread:
I had some issues with the cooling system losing fluid as well, but for a different reason:
Over the course of 3 months the car lost about half a liter (or quart) of coolant. There was coolant visible under the hood all over the left side of the 2.0l engine. Suspected the thermostat or waterpump. After 6 months I got tired of it and had the system pressurized to check for leaks. There are 2 small coolant lines which hook into the turbo, located on the front side of the engine, center left side, right next (left) to the heat shield. Checked the mercedes epc for parts and there are 2 small rubber seals (A0299973745 from the mercedes dealer) on these coolant lines, bought some new ones for 3 euro/dollar total on a gamble, and replaced them (easy job, remove the clamp, pull out hoses, remove old seals, lube the new seals and replace, clamp down) and have had no issues since.