Replaced today transmission cooler line
 

I both full line, for tranny to upper radiator outlet, at NAPA for 40$. I sorry I didn’t do that before then patch small parts of line one after another. Scary part is to open flare nut at tranny, rest was easier. Biggest mistake is I didn’t wash truck undercarriage before start work. Do not think about doing this job unless you have 5/8 flare nut wrench.

I replaced both cooler lines months ago. I should have removed the heat shields around the cat converters near the transmission before doing this, this would have greatly increased my ability to access the 5/8" flare nuts on the tranny.
I agree with the necessity of the 5/8" flare nut wrench.