I checked a GM parts site and didn't see the seal listed anywhere... Presumably, in that case it must come with the entire rail which said part is around $200. I could probably try a junkyard, but being that the youngest of these cars still has about 6 years of exposure to the elements, not sure if it's worth my time for such a brittle part. Not sure what to do now. Silicone? Duct tape? Foam in a can and a black sharpie? I kid...

If I leave it like this, I have concerns about water intrusion - does that seem valid? I don't know what's under the rack that would give water an avenue into places it shouldn't go.