>>1189696take the brakes off the bosses, spray everything with penetrating oil including the bosses, sand the bosses down a bit with a fine grit sand paper, grease the bosses and threads & re-install the brake. If that doesn't work, reinstall the arm that won't spring back into one of the more tense settings on the canti boss (uppermost of the 3 holes you see here on the bosses.) New cables and housing may help, or if you have one of those yokes with 2 stops on it, you could try switching which one you're using
Failing all that, you can try:
>>1189699 