I've just taken mine apart for another reason and had to remove the coiled spring inside. The coiled spring is what makes the cord retract. It's located just underneath the pull cord, so you can get to it quite easily. Just take off the four bolts on the top where the pull cord is. Once you remove that top piece, turn it upside down and there's one more bolt to unscrew the centre piece. pull this centre piece apart from the pull cord mechanism, but do it very gently, otherwise the coiled spring will bounce out and is quite tricky to reset. When you separate these two pieces you'll see the spring in there. Hopefully the spring is still intact and is just not catching the tooth that holds it in position. Have a look anyway... either that or the spring has cracked or split and therefore is not providing tension to make the cord retract. Good luck.
P Hegarty
April 2011