A area on a oak tree is usually remnant of hypoholon canker. Most times the barks just shale off after severe infections.
Kiril is right.................there has not been any proven evidence that tree tars, paints,etc. has been effective against preventing and treating tree wounds. It is used more for aesthetics than anything. A tree will callus around any wounding just as your skin. Oozing and foul smelling sap is just as our skin.......it is done to remove bacterial, foreign matter internally. Either the tree will naturally heal or it will become worse.