OK, my turn has come. My 87 W124 has coolant leak and it took me a few days to find the source. I do not know what the part is, but for those who are familiar with the W124 will likely know what I am talking about. The leak comes from a hose running next to the plastic over-fill tank and then disappear into the firewall right behind the tank. This particular hose has an electrical component connected to it and the leak is coming from the end of the hose where it meets this gadget. The bottom of this electrical gadget has a hose that runs to the front of the car and connects to the radiator. I squeezed these two hoses and I could hear water sound somewhere in front of the car and that makes me believe all these hoses are cooling system related. The leak is a fine mist spraying toward the manifold and seeing the steam is how I identified the source of the leak. My question is, do I just replace the hose? Replace the entire over-fill tank and all connecting hoses including the top ones to the radiator? Need some advise before this becomes a major headache like stranding me on the side of the road. The leak is rather bad and one side of the car is soaked.

87 W124
95 R129
98 W163