That branch likely is infected with a fungus, many of which are called cankers. Fungi like verticillium that is renowned for afflicting Japanese maples gets into the xylem (wood) and clogs the lumens. This means the leafs cannot get enough water to replenish what is lost by normal transpiration, so they loose turgidity or wilt. Shortly thereafter they will turn brown and hang on the tree (they will not drop because leaf abscission requires life processes that no longer exist for the lack of water).
Fungi like nectria canker infect the cambium. When the cambium dies a phytohormone is produced that causes living tissue in the wood to clog the xylem lumens. This process is a normal damage response (for pruning, say) just on a massive scale. The pathogen causes the cambium cell walls collapse and makes the bark a blackish oozy mess which will dry in time leaving a canker and everything above the canker dies in a similar fashion.
Regardless of the specific canker affecting your branch at least part of the solution is to remove that branch - all of it down to the crotch where it originates. If there is more tissue below that is obviously infected, remove the bark to the point that you believe the remaining tissue is healthy. Then, lightly burn all the exposed wood with a butane torch (even the little kitchen gadgets for making creme broulee are enough). This cauterization should kill any residual canker.
And yes, carefully and properly dispose of the removed branch and bark, of course.
And I advise that you spray fungicide, such as Daconil, around the area several times over the remainder of this season (attempting to nix spores).
And, be certain to sterilize your cutting tools afterward - I recommend 70% isopropyl alcohol.
The question I cannot answer is whether, in the longer term, there is enough well-structured tree left to keep. If you decide to keep the tree and not remove it altogether, another season or two will clearly tell how successful any attempt to save the tree has been. If there is any residual tissue infection, the effects will return!