Hi C2j,
I've just spent quite a lot of time polishing it up and I'm going to work out how to reconnect it to the mount. The thing is, it does seem to be hand made - to a very high standard but still hand-made. And it is SO light. I would like to think it must have been made by someone at de Havillands and presumably of aluminium from the works. And yes, the mounting arm failed at its most stressed point and does appear (to my untutored eye at least) a little crystallised. So maybe it was fatigue!