Finally replaced that original MB Waterpump today with a new one. Old one did look very good inside and I could not see any signs of corrosion or impellor degradation. No play in pulley either. Installed new one and started car. Same amount of pressure and coolant flow felt on top hose as with other pump. I was able to easily blow through the radiator top and bottom with no restriction while everything was off and drained. Could it be in the engine...??? Fan clutch works fine. It has been consistently in the 100's out here but when it drops to 85 degrees outside or lower, temp gauge reads between 80 and 100. Otherwise, it's right below 100 and climbs to 105+ when sitting at lights.