I don't know how well this would work on an exterior application, but in the world of furniture making a remedy to oozing pitch on resinous wood is to coat the trouble spot with a good coat or two of shellac. shellac can have just about anything put on over it and can be put over an oil finish if that is indeed what is already there. The shellac will form a hard shell (hence the "shell" in the name) that the pitch can't come through. This works good on pine that is to be painted (pitch will stain the paint and also prevent it from adhering to the wood, causing it to peel) or coated with poly or some such
