Tony. I have been watching your progress on the roof with interest, as when I was tracing how rain water was getting into the boot of one of my Dolomites, I discovered that if I used a hose pipe to spray water onto the roof so that it just went into the gutter it found its way inside and then ran towards the back of the car and then passed down inside the D panel and dripped onto the inner rear wheel arch. Then it ran down into the boot and I suspect some also found its way to the front area of the rear wheel arch. I proved it conclusively by putting some masking tape over the roof gutter and repeating the test. It seems it is critical to seal the joint between the roof panel and gutter. Do you agree or have I got another problem? Could this be the cause of why many Dolomites suffer from getting rain water in the boot? I suspect it could also run forward and down inside the A panel and so cause rot below the windscreen.
I know that you will not be working on the front part of the gutter but I also found on another of my cars that I was getting rain into the car, because the A panel to the gutter was not sealed very well. See photograph - Roof gutter by front windscreen.