Nothing to do or can do. Cherry is not a very decay resistant tree and one that age will likely have other pockets of decay in it. It has a good callus roll closing over the wound and there isn't anything you can do to prevent further decay. The seepage is likely slime flux from a bacteria that will live in old wood, again not a concern. Understand that this is a weak spot on this tree and a risk assessment of it failing (an Arborist on site would be helpful) if it is a valuable tree. Otherwise you should consider the target if it should fail, going to fall on the house, an area where you park the car, the kids playset, or the shed that is full of junk that should be thrown away anyway. Just joking about the shed, that's my shed.