Hi Bob,
All I can say is "do it now". Either replace with dyneema or S/S wire as I did. Our cable snapped. Luckily when the keel was down. We had just bought the boat. It had been surveyed and the keel winch had been serviced and inspected by the yard only a few weeks before. Just pressed the button to wind up and "Bang". Had to pay for lift out and yard assist to push keel back up to get reach eye bolts. On inspection the cable was spiky, but only the last bit rapped around motor drum where it broke. For the sake of about £15, I am going to replace it every couple of years or so, just for peace of mind. A failure from fully raised is your worst nightmare!
Do it as soon as possible.
Best wishes
Graham Ebb
Betty Blue 285/61