This is for a 1983 240D again.

I have a slow leak(a couple of cups a week) in the engine coolant. This is my daughters' car. I assumed it was the water pump, but there does not seem to be any leakage there. The radiator cap is new. There is no oil in the coolant or coolant in the oil. I cannot find any coolant in the passenger compartment and I do not see any leak in the engine compartment. There does not seem to be any hissing or other unusual noises when I shut the car off.

Anybody have another guess as to where it might be leaking?