I'm just a DIY'er, but can't help commenting...If you are certain that this is coolant leaking out at the ATF fitting, and Gilly is correct, which I'm sure he is too, then isn't it likely that the leak is coming from around the fitting, not from inside the copper tube or fitting itself that contains the ATF? Perhaps this can be repaired with JB Weld or something, if the rest of the radiator is still in good condition...just a thought

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1986 560SL
2002 Toyota Camry
1993 Lexus