Hi Darren,
1276 is a beauty - and would well deserve a extensive photo shooting and post!
Congrats! It's an absolute drem piece for anybody interested in the history of horology.
Not made during the best times of Breguet - but with this movement and humble case/dial - it's perfectly in line with Breguet tradition.
The sales date is quite funny - and wouldn't be surprised to learn that it was somehow "on purpose" , just to get some better numbers at the end of the year...

I gues it's been not the best times economically for Breguet during that period.
As aready suggested - crown mst likely isn't corect, as IMHO the seconds hand.
Together with a new more appropriate crystel and a good cleaning/oiling would be all I'd do ....
A real Beauty!
Best regards
Suitbert