It's difficult to determine the original cause of sap oozing from the photos. It could be a phenomenon called slime flux, or it could be a pathogen infection or an infestation of wood-boring insects under the bark. We recommend you consult a certified arborist to assess the tree in person. You can use this search tool to find credentialed candidates: https://www.treesaregood.org/findanarborist/arboristsearch

"Healing" it is probably not possible, and there is nothing you can do yourself to directly alleviate this symptom, but some conditions are not as serious as others. So long as the heartwood isn't compromised too much as to increase the tree's fall/breakage risk (which the arborist can help determine), then a slowly-declining tree can still provide years of shade and wildlife benefits.

Miri