The drooping "seal" is just a look-good thing called vinyl trim. It is meant to cover the screw heads but it is not waterproof. Even though RV makers treat it like it is. :(
The aluminum corner trim can be the source of the problem. And by problem I mean leak, and rotted wood inside. Because the sidewall leg of the trim points up, it catches rain and channels it down to the flat portion. There you'll find wood, and screws going up into the wood. The rot begins from the bottom up. Pull that vinyl trim out, then remove a few screws. See if they will tighten back up, or what. If they won't, that's a sign of wood rot.
Caulking the edge of the corner trim is a great idea. In this case it's probably way too late to do any good though.
