........... and what was perplexing them was the canceling mechanism, looking at the old one compared to the newly delivered one the lugs that do the canceling are a significantly different profile - in the end they resorted to an angle grinder to modify the lug - it now works beautifully.
I have just replaced my indicator switch and had exactly the same problem. I had to remove about 2mm from the top of the rather nasty cast cam that is attached to the steering column shaft. I used a file (not an angle grinder!), and took the opportunity to file and emery it smooth all round. I think it was the roughness of the casting that caused one of the self-cancelling arms to jam and snap off in the first place. Now works a treat.