OK, job done, but what a pain. Even with the right size screwdriver, the stupid little plastic screws got pretty mangled, and even when they're out, you're still stuck with small metal dowels stuck in a horizontal hole and no way to push them out. Would be easy given the right sized magnet, or the ability to turn the car on its side, but I eventually got them with a hand operated vacuum pump and some rubber tubing...

The grub screws got completely mangled going back in, but the loose screws are now done up proper tight with added threadlock so hopefully I'll never be doing that job again!