Related (I assume) to the Date quickset. If it were not broken the post would be captured by what I think is the quick-set date actuator on the underside of the calendar works cap Likely that I reassembled it incorrectly & snapped the post when pulling out the crown (maybe)
Thanks, I think you're right, & complete with part number (leave it to the Australians to provide an answer in the middle of the night... ;-)