94 E420 M119 Leaking coolant from waterpump

[DRICHFL]

I notice that my 94 E420, M119 engine, has developed a coolant leak. I have not had the time to search out where the leak was coming from until today. At the bottom of the waterpump I notice a black tube that was disconnected from the pump. Below the waterpump this black plastic tube, I believe runs down to a reservoir container located in front of the engine block but above the oil pan.

Question: The black plastic tube is not connected to the metal tube stem at the bottom of the waterpump. Coolant is leaking from the waterpump from that metal tube stem only when car is park and never while engine is running as far as I know. Does this mean that the waterpump need to be replace because of leak or reconnecting the black plastic tube will solve my water leak problem?

I had the waterpump replace by indie shop about four years ago because I was just being lazy. The car does not run hot and waterpump does not make any strange noise.

Feedback welcome.