Any question answered...

They're the basic Miche ones, these ones. The main bolt really didn't want to come out, I could unscrew it but only with great effort, and when I tightened it back up it started shearing the threads. Argh.

You did take the grub screw out first, didn't you? Unfortunately, even if you did, the grub screw distorts the threads in the centre bolt, so it fucks the soft female thread in the brake centre-arm as you take it out.