stain on tree bark
The black stain looks wet and sappy. We cannot see what is occurring underneath to cause it. (You could clean an area and send photos.) So we cannot say what is going on.
The foliage looks healthy. There could be a general environmental problem. Look through this fact sheet: http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG86%20Com...
We would recommend that you pull mulch away from the base. Mulch should never touch or be piled on a trunk. Also, we cannot see that the trunk flares out as it goes into the ground. The trunk should not go into the soil straight, like a lillipop stick. It should flare out. Pull back soil until you see flare.
The oozing could be caused by borer damage or some type of disease. There is no cure for this type of damage in a tree trunk. If the foliage of the tree looks healthy, enjoy the tree for the time being and then have it taken down when it starts to die back and decline. There really isn't much more you can do. If you want to have another opinion, you could contact a certified arborist to assess the health of the tree on site. You can find a certified arborist at the International Society of Arboriculture's website: https://www.treesaregood.org/findanarborist/arboristsearch A certified arborist has training in evaluating overall tree health and can make recommendations for you.