that seal just pulls off, theirs a part number on it, they aint expensive either, you wanna remove it as you have a major rust problem going on, treat it with the rubbe roff then paint it, as that metal is sooooo thin once a hole starts it will basically take over and their will be nothing left of that part of the door
you can remove it without removing the door, the support unbolts and retracts (10mm spanner is all thats needed)