Looking for a gas cap gasket for a 2000 Impalla instead of a $29 gas cap.

I'm also not sure if replacement caps come with a tether. I'm not sure how removed. Cut and insert a new one tether in a one way type mode?

It looks like an O-ring, but isn't. Looks like 2 1/8 OD, 2 1/16 ID and about 0.2 to 0.242 W, but it has a channel cut on the outer radius.

If this was Toyota, the gasket would be replaced as part of a service. If it's GM, your throwing a perfectly good gas cap in the trash. What kind of mentality is this anyway? This makes me want GM to fail.

The gas cap will come with a tether if it was originally equipped with one.
Call the after-market parts stores to see if the gasket is available by application. Ask if the will guarantee their new seal oncle installed.