It appears that the tarlike substance is oozing from an old injury that has "healed" (cambium and bark has grown over and enclosed the old wound). Likely there is some decay inside and the tree is "compartmentalizing" the decay at the boundary between live wood and dead wood. The oozing material is likely related to this, though I cannot tell exactly what it is from the photos.

For further assessment of tree health, we would look closely at the whole tree and ask:

Is the crown (branches and foliage) healthy overall, did the tree leaf out fully and have healthy green foliage for most of the summer? Or were there signs of decline such as dying branches and foliage?

How large is the area of the old wound relative to the circumference of the tree?

Are there large voids from old pruning or breakage of large branches? Are there fruiting bodies of fungi growing out of the stem or surface roots?

For our native Oregon white oak trees, internal decay from wood rot getting into old or injured roots is a common cause of physical tree failure.

For further diagnosis at a distance, you could send me more photos of the whole tree and parts of the tree.