Curta's are a special case, I'm not a watchmaker and I wouldn't dare to try at this point in my skill progress, but for example I had some sprocket wheel ones for which I made new cogwheels, pouring rain with powder in it or casting it in brass and filing it down. But Curta's - I don't know. Maybe if it's the last chance, but what kind of insane SOB brakes a curta? :)