That sounds like my moms tree..I noticed also that some of the branches have spots were there is a lot of thick sap, looks almost like honey. I am not sure why that is happening either. I want to try to save this tree if we can, it seems to be having a pretty rough go.
RR
There is a way to help extend the tree's life, and that is by cutting out the damaged bark. You'll need a sharp knife, even an exacto knife would do for this job, and a short length of a metal coat hanger!
Start cutting where the bark looks dead and cut back to where the cambium layer is (that's the live part between the bark and the live wood)
You may find holes in the wood, so you can use the section of the coat hanger to stick into the holes to kill anything that is inside, usually the larvae!
Then you can start the pesticide treatment.
There is no need to cover this exposed wood as tghe tree will heal itself and grow around the damaged wood!
If there is damage further up the tree, you can cut around where you find the dried/or oozing sap! You will more then likely find one or more larvae feasting! Just cut back and clean the area out and examine the area for any tunneling. If there is, you can use the hanger to poke and clean out any tunnels.
This method will take time and the tree will recover as long as you use a recommended pesticide. Your tree will love you for the effort!