I apologize for the strange post. I couldn't find a name for the lines in my Bentley manual--you may be correct that it is the tranny cooler lines. There are two of them, one at the top, and one towards the bottom that eventually run side-by-side toward the tranny. I'm not real knowledgable about the cooling system (obviously).

I checked out my other bricks and this nut is unusual (there's one on both the upper and lower line). I will swap the radiators this weekend.

Many thanks for your input!

Milan