33 Roof Insert

[Kpar]

Just spent a 3 day weekend away with Fords (& others) Had a few showers of rain and for the first time got a couple of leaks on two of the corners.
Before I attack it some advice on how. It's obvious that the joins have let go and will require refixing. I'm a bit reluctant to pull the lot but maybe I'll have to. Any help?
sorry pictures must be too big not sure how to reduce them.