Changing the core wire will not change the tension nor breaking % appreciable but ti will change the inharmonicity a good amount. I would just call Mapes or Schaff and tell them the make and model and serial number and have them make replacement strings to the original scale. I don't think the components of the strings were at fault. More likely a nick at the pin or other causes like poundingf\ that note into daily submission. Newton
This PTG archive page provided courtesy of Moy Piano Service, LLC