Based on the symptoms and timeline you described, a borer infestation is very likely, particularly given the tree’s age. Geriatric apricot trees are especially susceptible once they become stressed. The progression from reduced leaf size and weak growth to visible sap-covered holes in early spring strongly suggests that larvae have been feeding internally for some time before the damage became obvious. The fact that the gumming started at the base and has moved upward into large scaffold branches is a classic pattern for borers that attack stone fruit.
    The most common culprits in apricot are peach tree borers or lesser peach tree borers. These insects overwinter as larvae beneath the bark and resume feeding in early spring, which aligns with your late-March discovery. Sap mixed with sawdust-like material indicates tunneling beneath the bark and into the cambium. While other borers are possible, the location of the damage and the presence of gumming make peach tree borers the most probable cause. Confirmation can be done by carefully scraping away sap and loose bark to look for larvae or probing the hole to detect tunnels.
   Immediate action focuses on limiting further damage rather than fully curing the tree. Heavily infested branches should be pruned well below visible damage and removed from the site. Chemical treatments are preventative only; trunk sprays applied later in spring and summer help stop new eggs from hatching but will not kill larvae already inside the wood.
   Long-term success depends heavily on reducing tree stress. Deep, consistent watering, avoiding trunk injuries, moderating fertilizer use, and protecting the trunk from sunscald all help make the tree less attractive to borers. Given the tree’s age, recovery is possible if damage is limited and the main trunk is not heavily girdled. However, if infestation is extensive or the canopy continues to decline, removal may be necessary to prevent borers from spreading to nearby stone fruit trees. Hopefully this helps. Best of luck.