68 Dart Rear Pillar issues for repair

Hi All,

I have a 68 Dart that has some issues at the bottom of rear pillars where they meet the top of rear fender. Please refer pics to see that I either have rotted sections, and/or the metal has simply split apart internally, where the lower drip rail trims attach.
I was wanting some feedback if possible about this damage -
Is it normal/common for this occur on these models?
Best method/s to repair this damage in preparation for a near future colour change paint job?

Thanks in advance for any assistance!