Answer: Aphids typically cause the leaf symptoms you describe, but horticultural oil sprays usually take care of the problem so perhaps your sprays were ill-timed. As for the oozing fruit, there is a species of weevils called the plum gouger (Anthonomus scutellaris) which is particularly common in the hard European plum varieties. These weevils spend the winter in the adult stage around the base of previously infested trees. In spring, about the time blossoming occurs, they move to the trees and feed on the buds and flowers. Later they feed on small fruit, producing puncture wounds.
Wounded plums typically ooze sap. Eggs are laid in some of the fruit and the young beetle grubs develop on the pit of the fruit.
Effective controls have not been identified for these pests. They will often drop from plants when disturbed, so some beetles can be collected by shaking branches over a sheet during blossoming and fruit set. Fruit tree "cover sprays" applied before and after bloom should also control them. You'll also want to destroy the fruit to get rid of the eggs and grubs that will become the next generation (don't leave the fruit lying on the ground).
Good luck with your fruit tree!
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