wabiola

I own a Mercedes ML 400 since last November; I found a leak in the coolant. The liquid flows through the drain overflow of the expansion tank. My Mercedes dealer tells me about the change of engine after checking, radiator and water pump.
My car has only 85,000 KM like to know if anyone has experienced a similar problem or have an idea of the origin of such a problem.
I'm not ready to invest in a new vehicle.