I need to replace the transmissiom cooler attached to the radiator of a 99' dodge stratus 2.5 liter 4dr sedan. The right line snapped off leaving a small hole in thetop just below the nut. I can't get the nut unscrewed to replace. Can you tell me what to do?

Optional Information:
1999 Dodge stratus

Already Tried:
vice grips. box wrench and wd40