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AnswerLooking at both pictures this is an insect called a oak borer. They attack the tree and bore into the bark and sap will run our causing the wet dark areas. usually borers attack trees under stress and looks like this tree has many attacks. In this case it seems most if not all the foliage is dead and based on the number of attacks in the bark picture I am afraid I would agree that the tree is dead and should be removed. I would check other oaks nearby and if you see the dark wet areas on them they can be treated with an insecticide to kill the borer under the bark. You can spray an insecticide on the bark of the oaks where the borers have entered and this will kill the insects under the bark. Use an insecticide called Onyx or Merit. Check with your local garden type store for these.
Stress can be caused by many things--dry weather or lack of nutrients in the soil are a couple of them. I would expect that your area has experienced drought like conditions this past year or so. Not much you can do in this situation but try to reduce the borer population with the insecticide spray. I would suggest fertilizing the trees with 10-10-10 fertilizer at the rate of 1 lb of fertilizer per inch of trunk diameter scattered around the tree and watered in good, Apply just before a rain storm and you will not have to water. This is ok for the trees around your house but would be too big a job and expensive for all the trees on a large acreage
