This resembles a phenomenon called Wet Wood or Slime Flux, and by itself isn't very serious, but if the tree canopy appears to be in decline or if you're concerned about this symptom worsening, we recommend having the tree evaluated by a certified arborist. They can help to diagnose issues as well as look for sources of tree stress that might be able to be alleviated in order to prolong a tree's life or improve its vigor. While arborists can't treat or cure every condition, some do have specialized training regarding assessing hazard trees if internal wood decay is suspected. Some arborists are employed by tree-care companies but others consult independently in case you were wary of recommendations for costly or unnecessary treatments.

Miri