Ho My goodness Pookapelli, what on earth has happened to the poor tree, the damage was not done yesterday that's for sure EH !!!!.
Not a lot can be done would be my real answer, BUT, I'm not really one to ignore a challenge or help / try to save something that has put up a fight for years to try survive.
The best way I know to help the tree is unfortunately NOT what you may want to hear but here goes anyway.
The first thing you need to do is remove the strain from the large lower branch, on the 1st picture that is the branch on the right hand side and is lower than the Y shaped left hand branch.
It's NOT a case of just cutting up the branch, there is a proper way of doing this without causing the branch to split further and if that happens, the weight of the falling branch will cause even more damage to the best of the other leading part.
Either use a hand saw or a chain saw, (with protective clothing, boots and gloves, also goggles to protect eye's.
ON the lower branch 1st picture, look at the wire / cord, rope ??? and about 2 feet from the rope, make a cut below the branch the underside ( that is your cutting upward) dont cut through the branch, just about half way, then next cut is on the top side of branch, ( dont cut right above the under cut) you need to make the cut about 2 inches past the lower cut, when you do this 2nd cut, the branch should fall to the ground, all the strain being put onto this branch will be gone and the good, left hand leader will be able to keep growing, will send out new shoots and in a year or two you will have a perfectly good growing tree again.
IF you cut the branch from top only, the cut will cause the branch to split half way through the cut and it will tear the branch apart due to the heaviness of the large branch, but cutting under it will mean the weight is not going anywhere till the top cut is made and it falls clean away.
You must remove the rope / string / wire or whatever that is wrapped around the trunk, it is beginning to cut into the new flesh of the trunk and it is allowing diseases to attack the good part of the tree.
After you have removed the heavy lower (right hand branch) I would then make another cut and remove the rest of the right hand branch lower down until you remove the brown damaged part of the trunk, when you cut that close to the trunk, always make the cut so the cut area is sloping downwards and allows any rain water to run away from the damaged trunk, water left sitting on a wound is not a good idea as more rot will set in and so could disease.
This work should be done when there is NO sap rising, so autumn when leaves have fallen or very early spring before sap begins to rise as IF you cut large branches like you have, there is every chance the wound will seep out sap and insects will flock to this maybe bringing infection or diseases, some folks paint stuff from garden store onto cleaned up damaged branches to help heal the wound but, new thoughts are to leave well alone and allow air to help heal over the wounds. it has worked here so I would NOT paint the area, let nature do it's job after you help fix the problem and save this lovely tree.
Good luck. WeeNel.
The tree guy where I bought it said about the same thing. I shouldn't have let it go so long. It's where I want it to be at this time. If this does not work I'll just have to start over.