oneclick : thanks - that is clearly what is wrong. Not sure why it was working before unless it was cracked and fell apart when I removed it several months ago to start the cleaning process. Is the assembly in your picture still available from some specialist shop? If not, I am thinking perhaps drilling a hole through the threaded portion for the cable and just squeezing the cable between the arm and the nut.....if all else fails look for a replacement derailleur.....