^... the only one that I was asked to look at by a clubmate, who wanted me to check how he had wired it as it wouldn't spark. There was nothing wrong with his wiring but I decided to try it on my regular use bike, substituting it for my working CDI, but couldn't get a spark on mine either. Then, in trying to ensure that the HT lead was contacting correctly, I rotated the HT lead gently to ensure it was home and I too sheared the contact pin/screw as described above.
I really like BGM's stuff (their stators have done wonders for Lambretta reliability) but they seem to have been let down by their manufacturer in this case

The CDI was replaced with a standard one, without any fuss, so no complaints about service either.
Adam