Have you pruned or cut the branches recently as this can cause them to bleed if done when not dormant.

The tree is fully grown, a small branch was cut off many years ago when the tree was smaller but is now ouzing sap from where the branch was removed

The only thing I can suggest is you clean the area where the branch fell from if it is not a clean break and apply a wound sealant that you can purchase from any garden centre. Hope this helps.