Hull / deck repair

[djd]

Hello,
I'm working on a Daysailer I (Hull No 18168, Class No 3320). There is some damage on the starboard rub rail, near the transom. Looks like it must have banged up against a dock or piling and broke off the rub rail mounting flange. (The lip that sticks out where the hull and the top side meet.) Someone made a rough repair long ago, but it is breaking away.

I removed the white rubber rail cover and under it is a grey, PVC strip stapled to this mounting flange. Can anyone offer advice on how to replace the flange in the damaged area? Can anyone tell me what a cross section of this hull joint would look like? Is the flange part of the deck or part of the hull mold?

Any help would be appreciated!
Thank you,
Dennis