It's been a number of years since I did any "vanning" and the water ingress problems do not seem to have improved much. My father had similar problems with several vans ranging from new to around five years old. We even took some of them back to the manufacturers (East Yorkshire area as I recall) and watched the repairs being done. One van was virtually reskinned!
In the end, I just gave up and went back to renting a holiday home! It turned out to be more economical (albeit less convenient).
I hope all goes well and that a settlement is forthcoming.
You would have thought that they could have sorted the sealants out by now. It's amazing how much bending and twisting goes on in those joints so it needs to keep flexible for years. Not an easy job keeping water out as any 75 owner will tell you!
Mike