I've had that exact same door on my '99 Marquis fail as well, both skin and frame. I guess since its likely the most used door.
One of the welds failed on the top corner of a cargo door frame and I was able to take a piece of aluminum angle and cut it to size. Drilled pilot holes through the angle and frame. I then used self tapping heavy duty sheet metal screws I had left over from a cargo trailer project to screw in place. Still holding very well.
Took the door off to do that so I could clamp it square. There are some retaining blocks holding the top door lip, but you can remove and then push the door in when raised (and struts removed of course) in to allow it to drop down free of the door frame. Best as a two person job or carefully with stands underneath so you do not drop the door.
I would certainly prefer to reweld, but that then involves removing the door skin or likely repainting due to collateral heat damage from the weld.
If the skin is coming loose from the door frame, then it is the adhesive failing and the skin needs to be (gently) pulled, existing adhesive removed and reapply using some of the construction/vehicle grade adhesives before reattaching the skin.