Alison, Sorry to hear about your fruit trees.
If the gum is coloured, it's probably a bacterial canker (especially if the leaves, before they fell, had necrotic spots on them which eventually dropped out leaving little holes).
If the gum is absolutely clear and sappy, it's more likely to be the boring larva of a moth, but it would be very unusual for you to have such an infestation.
There is a nematode treatment for the borer; I'm in Greece at the moment so don't have access to my Koppert bio control catalogue, but I'm sure others on the forum can advise.
If the problem is canker, my own inclination would be to scrap the badly infected trees and start again. Copper sulphate does control it to some extent; at least in the UK is not an "authorised" treatment for peach-family trees, but as it is authorised for control of leaf curl there, there's actually nothing to stop people using it, thus keeping leaf curl at bay and at the same time fighting the canker!