I wanted to follow up on this topic and share my experience of the procedure in hopes of helping anyone else looking for info on the topic. It took me about 5 hours from start to finish but if I had to do it again it would likely take no more than 2.
The replacement part was ACDelco 15212982
I didn't need to buy anything else as the leak was directly in the line and not at one of the connections. Anyway, here are the steps that I took:
1. Remove air deflector panel underneath the radiator to gain access to the transmission cooler lines.
2. Remove the nut from the transmission side bracket that secures the cooler lines to the transmission. Pull the bracket/lines out of the transmission and have a catch-pan ready for any transmission that comes out.
3. Detach the white retainer clip holding both lines to the frame.
4. To access the nut connecting the lower line to the radiator, remove the radiator support mount that's just below it. It is attached to the frame with two bolts. Remove them and then wiggle and twist the mounting bracket off. This can be a bit of a pain because a plastic panel immediately to its right constrains the bracket's motion when you're trying to remove it. Removing a few plastic clips will help by allowing you to pry the paneling back. Once you've reached the nut, remove it and have your catch-pan ready.
5. Next you'll need to reach the nut securing the upper line to the radiator. If you remove the outlet duct you can easily reach it from the top, but to remove the nut you'll need either a crowfoot wrench or something else that will allow you to unscrew it from an awkward angle. Since I only had regular open wrenches available, I removed the right headlamp completely to gain access to it.
6. Remove the two radiator connector nuts from the lines. There is a black plastic retainer that first needs to be popped off followed by a metal retaining clip that can be removed with tweezers or a pick. Once both retainers are off, twist the connector nut off of the lines.
7. Install the connector nuts onto the new lines along with the metal retainer clips. The new cooler lines will come with already come with new plastic retainers.
8. Fit the new lines into position under the car. I installed the transmission side bracket first, then the white clip, followed by the lower radiator nut, and finally the upper nut. Be aware that when you go to screw the lower nut back into the radiator, the piece that it threads into will give way and fluid will drain out until you fully screw the nut back in, so have the catch-pan handy.
9. Re-install any parts you removed (e.g. radiator support bracket, panels, etc).
10. Remove the 11mm plug from above the transmission oil pan to get ready to check fluid level when topping off ATF. Remember to top-off while the car is running.
I'll try to remember to add a few photos to this description when I get a chance.