I seem to have 'lost' the sticky bit off one of the front brake pads. Don't ask me where. I'm sure it was there earlier. And then I rode the bike round the block a few times to test it before its MOT. And after a little while there was this funny scraping noise under braking. So I tested the brakes a bit... The disc is a bit scratched on the outside edge. Salvageable? Also - can't undo one of the retinaing pins in the caliper to get the bloody pads out. Any suggestions?