I'm repairing a rusty Seahorse that belonged to my grandfather. I've freed the mechanism and given it all a good clean and removed any meaningful rust. The hairspring's snapped near the stud and the stud screw is rusted solid. I looked into getting a new balance assembly, but Cousins (UK) says they're obsolete (part 310.660). I understand this movement had many variants, so is it at all possible to get an alternative balance that will work? Or is it time to delve into De Carle and make my own repairs? An approach doomed to failure, I warrant...!