[dtw]

I spent three days getting two nuts off mine. Alternating penetrant, hammer blows, and heat. They did finally come off without destroying the threads. Mind you, this is on the bench, after tearing the entire oil cooler system out of the car.

If you don't mind re-brazing the ends onto your lines and you can find the correct compression fitting nuts (Chuck Moreland can probably supply them), you can just carefully cut the existing nuts off. I did this on a line that was already destroyed anyway.