Q.What do I need to do to keep tree healthy
The trunk of my peach tree bark is splitting and it’s oozing sap. In one area on the trunk, the flesh of my tree is showing and it has a large crack. What do I need to do to help my tree?

What you are seeing is gummosis - it is a gum/sap that oozes in response to injury, whether by insects (peach tree borer), mechanical injury (such as by pruning), winter damage, or virus/disease.
Below are links that will assist you in diagnosing your tree. The Cornell fact sheets will also help you in repairing your split bark.
(Cornell Univeristy PDF - cankers on trees): https://bit.ly/1E6AIAN
(Cornell University PDF - bark splitting on trees): https://bit.ly/1KEmrRn
(Cytospora Canker) https://www.gardeningknowhow.com/plant-problems/disease/weeping-amber-in-trees.htm
(Peach Tree Borers) https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-borer.htm