Maple tree cracking
Glad you sent the pictures.
The sap flow is due to the wounding and cracking from the Co-Dominant Stems.
Whenever trees form two leaders (trunks) from co-dominant stems and they are attached at a tight V union, the bark gets compressed between the stems and there is no grafting of these unions. As the stems get larger in diameter, they apply pressure to each other, forming the crack and sap follow. These co-dominant stems with included bark are a very weak union (or attachment). They are starting to split apart and we often see one of the large stems break out in a storm.
It is probably too late to fix this problem because the crack is there. Having an ISA Certified Arborist install a cable above might help prevent the stems from falling apart in the near future, but the defect is still there. It is so important to properly prune trees when they are young to maintain 1 central leader with smaller branches forming off of that leader (like a pin oak does on its own).
For more information take a look at Dr. Ed Gilman's tree pruning website - http://hort.ufl.edu/woody/pruning.shtml