I had to smash the dial apart (using a pair of tin snips and pulling the bits away with long nose pliers) making sure that I didn't break any of the assembly underneath.
Then I removed the d-washer (the dark one) by pushing it to the side being careful not to let the spring fly out.
The whole assembly then slid out easily and I saw the the teeth on both the dial and the receiver are worn (brittle plastic after ten years of operating I guess).
I hope this helps if you come across the same problem.
Stuart
April 2006