A new o-ring may seal it. I keep a spare fitting in my back up parts box. My coolant leak was the lower oil cooler seal. The cooler would teeter due to vibration. Once I secured the transmission lines from moving too much, the leak stopped. Try securing the hose line a bit to limit movement. Or did it crack?

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'06 X5 3.0i - bought @143,123 miles (12/26/20)