After using more force than necessary to get my driver side door to close, I actually noticed that the gasket is loose. This is on the top right portion of the door.

I have been moving it back into its normally seated position, and this helps.

I tried to get it remounted, but I don't seem to notice any particular grooves of flanges that are supposed to hold it in place. It doesn't look torn either.

Was it originally glued in place of something???