Your gable roof vents are usually made of vinyl, which is a type of plastic. Most all gable roof vents are manufactured with a UV Stabilizer that is mixed in while it is still in liquid form. Once the vent is formed and cured the stabilizer helps to prevent the vinyl from breaking down when hit with the suns harsh rays.

The stabilizer only slows the decay and eventually the vent becomes brittle. Once these vents become brittle, they are prey to the wildlife such as squirrels and birds and eventually end up with broken and missing fins, which allows animals and insects to nest in your attic.

These vents allow the extreme heat of your attic to escape into the outside air. This is important because it prevents the attic from sweating; if your attic sweats too much, too often, mold and rot can form, often resulting in catastrophic damages.

This video will show you how to change out your vents if you have a vinyl siding home. If you have aluminum, it's much more difficult because the aluminum can easily bend, but the process is much the same. If your house has the old fiber boards (asbestos siding), you should replace that siding with cement boards instead.

All of the links you will need to perform this repair are right here for you:

Gable Vent (24" x 30")
https://amzn.to/2NzF3yT

Siding Removal Tool
https://amzn.to/3vL6eYu

Werner 40' ladder
https://amzn.to/3eWCthv

Ladder standoff
https://amzn.to/3eWDTIV

Cement Board Replacement Siding
https://amzn.to/3qXbR2o

GoPro Hero 6
https://amzn.to/3cMI6fD

GoPro Head Mount
https://amzn.to/2P7769k

GE 100% Silicone - Clear
https://amzn.to/3tCoa5N

Good luck with your repair and be safe,
Bob