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So you're looking in the correct area, there is a damper assembly located behind the back panel inside the freezer. If you pull the drawers out at the bottom of the refrigerator you'll see the damper assembly. Below is a link to the damper assembly so you can see what it looks like and this part needs to be replaced. The masking tape is just what they use for styrofoam---that is normal.
CLICK HERE for damper assembly
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You can't really confirm for 100% certain it's the problem by inspecting it. If the refrigerator is too cold then either the damper is bad or the sensor is bad. You can't test the damper but the sensor is behind a little 2" white plastic vent in the side wall of your refrigerator near the back somewhere. You can cut this sensor out and put it in ice water to test resistance through it to see if it's good. It should be 16.3k Ohms and if so then the sensor is good, otherwise you need to replace the damper.
Yes the damper should just lift out when you remove the screw but it'll be stuck pretty good usually.
Yes, the sensor tells it when to open or close based on the temperature inside the refrigerator.