Puckers

I own 2018 BMW Series 4 convertible. I noticed water sloshing around in the rear panel of my two door car. We took it to the local dealership who confirmed that a vast amount of water had collected in the rear panel rendering the roof and window inoperable. We can see others who have experienced the same issues and wondered if they have had any success in getting BMW to acknowledge this as a design fault and pay any compensation. The cost to us for rectification which included new drainage system was £1000. We have tried all avenues to further our claim and met with a dead end.