To Start Over or Not?

Sounds like replacing it is the right thing to do. Sometimes when you replace a section and over lap them you do end up with a gap between panels. What I do in that case is put seem sealer between the to panels in the gap and then close the gap up with a big Fning Hammer, LOL. Then I spray it with rubberized under coating.

The 1 piece panel is going to take a lot of time to remove all the old spot wels and fit the new panel but it will be worth it in the long run.