I replaced the refrigerator damper per your online diagnosis when the refrigerator is too cold -
ours was running at 30F. I watched the video which greatly aided the install. Our refrigerator was slightly different with more ducting down the back and two additional ducts on the ceiling of the refrigerator. But the video helped understanding how the parts came out. I had to remove two plastic "door" pieces on the replacement duct so they would feed into the top ceiling ducts on my model. I also added some adhesive backed foam on my ceiling ducts to close off the opening to these ceiling duct openings on the replacement duct. The ceiling ducts come out by sliding them toward the front of the refrigerator and they are tricky to slide back in place. You must look on the inside edge to see how the tabs line up and then slide over corresponding tabs on the refrigerator top plate. No tools are required, you just have to futz with it several times to get them lined up and seated fully. If they are not fully seated and pushed back, the light cover will not snap into place on the front taps. I also slit the wire openings on the silicone weather seal in my original duct electric connector and added that to the new one.
Before I installed the new duct I pulled apart the old duct and sure enough, the door axle was broken as others had mentioned so this was clearly the problem. The refrigerator is now maintaining 37F per my setting. I didn't replace the Temperature sensor I bought.