Apple tree with splitting bark
I have a 20 year old Mutsu Apple tree that has been bearing fruit every year prolifically. This year the main trunk and a few main branches developed large cracks in August and watery sap leaked out wetting the bark around below the cracks. The tree has also developed a one foot square section of trunk area at the base of the tree where the outer layer of bark is dying leaving a brown crusty peeling bark instead of the silver smooth bark.
Is this a warning sign of some disease? I don't see any pests but the tree late in the season gets powdery mildew and has a small amount of fireblight this year for the first time. Does anyone have helpful suggestions of how to save the tree? I love the fruit!