11-01-14, 10:41 PM
Dismantle the plug caps and clean up the internal components. Look down the end and you'll see a crosshead screw slot ... that's your way in. 
Also, if you haven't already tried it, cut 1cm off the end of the plug lead to ensure you've got a good core-to-cap screw fixing.
Also, if you haven't already tried it, cut 1cm off the end of the plug lead to ensure you've got a good core-to-cap screw fixing.