First Jeep, got in barn trade.
lower cooler line rusted out, trying to replace.
How the hell do you remove the transmission side of the line?! What size nut is it, is there a specialty wrench I'm not aware of? There's like zero room to get a wrench in there! I know this seems noob as hell, first Jeep used to working on Mk4 vws.... Please help me get this thing on the road!

 

Welcome to the forum.

Please identify the vehicle year, engine size and transmission.

On my 46RH transmission both cooler lines are at the same height, one is in the front, one in the rear.

Be aware that a common failure is cracking the transmission case at the rear line, so be careful.

My front transmission line is difficult to unscrew because of the placement and all the surrounding stuff. The open end wrench only has a very limited arc, requiring R/R the open end wrench many times.

On my vehicle the cooler lines are clamped at the starter and at the engine block. I have found that removing the starter transmission line clamp makes it easier to R/R the transmission lines from the transmission case.

There is a rework fitting for the end of the transmission line, to discard the factory fitting and replace it w/ a heavy duty fitting.

 

Think out of the box, LOL! If your going to replace the line anyhow, cut the pipe off and use a box wrench. I figured that out when I changed an 02 sensor the first time. I cut all the wires off and used a deep socket. If you cut the pipe short enough, you can use a socket also. It's a little bit of a hack method, but it works.