Forgot to report back on this! lol Well, Jim and me stripped the whole rear interior out, which was a total nightmare! New cars just aint built to be taken apart by us!! We got there in the end though, then checked for water ingress. Didnt see exactly where it was coming in, as it's kinda in behind the inner metal of the rear pillars etc, so checked all around the window, and the seal around that is fine. So we decided to take off the roof gutter strip to have a butchers underneath that. Now I did read on civinfo that these gutter trims are almost impossible to take off without breaking either the trim or the clips. With my trusty plastic trim removal kit, I got it off first time, no damage!! The gutter underneath was seriously bunged up with crap, so cleaned it all out. Then noticed that the sealant around where the trim clips into place (there are bolt ends coming up through the roof for it) looked buggered, so cleaned it all out and resealed it. Did all the mounting points along the guttter then put her all back together. Result? Been pissing down with rain up here for the last week, and left her parked in the drive instead of the garage. No more wet seat belt!!! Yas!!!!