The light is definitely the source of the leak that caused the delam IMO.
I'm gonna be the odd ball I guess on the roof based solely on the video. It appears to me based off the video alone that the weakness shown "could" be caused from the roofing material going from the roof decking to the side over the trim causing a gap under it around the edge. Is the decking underneath solid? Also what kind of price or we talking? Is it priced right so that if some minor to moderate repairs are needed that it would still come in as a good value? Also, is the seller/dealer willing to warranty and or make the necessary repairs? I know you said its a consignment, so have it looked at by a third party inspector and ask for repairs to be covered or low ball it and see what happens if your happy with it.