Vintage Ancre 15 rubis identification

Hi all,

I am working on repairing my grandfather's watch - a vintage Ancre from around the 2nd World War. The watch itself has sentimental rather than monetary value, and it looks like the balance is having trouble keeping in motion for any length of time. I suspect that one of the pivots on the balance staff is shot, si I need to either source a donor movement or replace the balance staff. In order to do so however I need to know who the manufacturer of the movement was. I've taken a look under the hood but can't find any hallmarks or stamps, so all I have to go by is the lettering on the dial ("Ancre 15 rubis") and the engraving on the top plate of the movement ("15 jewels Swiss Made"). Is anyone able to help identify the movement, or give some clues as to where a hallmark may be?

Thanks in advance,

Kind Regards,

Jan