Finally I got it to work. I had to pare off some bits of the plastic socket so that it would fit in the tube. I used a small stanley knife and some emery board (or some kind of sanding board). Getting the rear break cable back in through the tubing was a bit of a battle but managed it in the end. If you shine a light in the little hole at the bottom of the rear tubing you should see the break cable descending. I used a little scissors to grab it and pull it out.
Quite a tough job, glad I was able to get it all done. Just took it out for a spin and it all seems fine.