There are two transmission coolant lines the run from the tranny to the radiator. On eline is an inlet, the other is an outlet. The tranny fluid is run thru the radiator to help cool it. These lines are usually just bolted into the radiator. Get a FLARE WRENCH and you can tighten the leaking nut. BUT!!! If it is tight, take the bolt out and you will see how it is, wrap some teflno tape around the threads in the opposite direction from which the bolt threads in and then START THE BOLT BACK INTO THE RADIATOR WITH YOUR FINGERS to make sure you do NOT CROSSTHREAD IT! You can do this to both lines. You will get some fluid loss so try to keep it to a minimum so you don't have to add tranny fluid back into you tranny.