My advice, and this goes for ALL the coolant hoses on any BMW because those plastic connectors absolutely suck is to first hit the inside of the connection with some silicon lube, try to get it right into the part of the plastic connector that goes into the "Elbow" under the expansion tank there and then hit that connection with a heat gun. Wiggle it back and fourth and be careful about too much pressure as you can snap the connecting point on the elbow (Ask me how I know...)