Geoff - thanks for the tips - I disassembled the unit, managed to remove the filament and cleaned the toothed gear - it was pretty clean. On reassembly it still will not feed - It appears that something is blocking the nozzle - I should think that the next step is to remove and clean the nozzle.
Your notes indicate that the next step is to drill out the nozzle - did you remove the nozzle before drilling? That is not clear from your description. I guess the hole could be drilled out while it is mounted but it makes more sense to remove it and try a solvent (acetone?) first.

Thanks again for your help.

dave