The trans oil cooler leaking coolant out on the ground can be either -

1) trans cooler body itself is leaking
2) junction between the trans cooler and radiator mounting plate

If the trans cooler itself is leaking, you'll probably have to replace it, about $150.

If it's at the junction, it could be as simple as the 2 x-rings that list at about $1.50 each.

Either repair is an easy reach from the bottom of the truck.

Clean the area up so you can pinpoint where the problem really is.

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04 X5 3.0i auto
03 X5 4.6is