RustyOlds

Another day another leak. Today's leak is on the lower transmission coolant line. It only leaks while the car is running and leaks about a drop every minute. I've heard online it could be an o-ring of sorts? Anyone have any ideas on this? Also is thread sealer a viable option on this? Thanks!

Fun71

That should be a flare fitting, so no o-ring or sealant. There could be a nick or burr on one of the mating surfaces.

oldcutlass

You might try taking the joint apart cleaning and reassembling. Do not use any sealer or tape on the threads as that is not a sealing surface, the end of the flared line is.

BlackGold

Don't just clean, inspect as well. When I bought my car the previous owner had installed copper lines. It leaked about a drip a minute, like yours. I thought I was smart to tighten the nut an eighth turn. When I started it up again, there was a geiser. Turns out the flare on the copper line was split; tightening made it worse, not better. Hope you have better luck. And if you have copper lines, replace them with steel as the factory intended.

65vistacruiser

Only late model Fords use an O-ring with an inverted flare.
Someone may have made single flares on your lines as opposed to double inverted flares. The double flare is thicker, no sealer needed.