The long and short of it is that when I had owned the car for two years (and did eight miles in it as I was doing other stuff) I decided to redo the interior. Then after getting it all out I cleaned it up and redid some of it. Then I redid our bathroom, sundry other jobs etc and three years later here we are. Anyway, I thought the two bolts holding the hatch strut mount were how it was fitted originally (although I do remember thinking at the time it was strange).
Anyway, as I now know, it is spot-welded but mine has obviously broken at some point and been fixed by the mount being drilled and attached by the bolts. when I removed the interior panel on that side it was all chewed up as long bolts had been used which went through the edge of the interior panel, with nuts and washers, eventually breaking the panel.
So I cut the broken piece out and set about making a new piece which I did roughly three years ago. When I came back to it this weekend I found it wouldn’t fit, so I used smaller bolts and inserted them from underneath. then I had to remake the piece using the old piece and recutting and refibreglassing behind it, raising it slightly. It’s not great but it’ll have to do.