I have a York central air system in my house, is 19 years old and was installed when the house was built. I do not know the model of the air handler. It has developed a leak in the evaporator of about 1# per month. Is this repairable (new core) or would the entire unit normally be replaced? It cools the house fine, even in the hottest weather, and I've never had an electric bill over $100, even last month.