Internal damage from battery leakage

Peter, you can clean all your parts in isopropyl alcohol. You can even try to remove the corrosion residue with a soft brush and a baking soda solution, after that clean all the parts with a high concentration (over 90%) isopropyl alcohol. As for the loose connectors etc, this will depend on your skill level. Most of the parts are SMD components and are surface soldered. The best way to fix those would be with a hot air station.