There looks to be some NiCad corrosion in the reset area near the battery (old Bally/Sterns used NiCad batteries) Typically the traces show a lot of eating away and all the components have to be removed, board sanded etc... - this one not as much. I venture to say most of the rest away from this area, such as the board mounting screws, is moisture related from the storage conditions

Neutralize the board corrosion as best possible using white vinegar, followed with a cleanup rinse of 91% isopropyl alcohol. Since the game boots you might get away with not replacing the components if the corrosion process has not penetrated the component bodies. I'd try some other rust remover, like Naval Jelly on the metal backboard and mounts and replace all the rusted screws for for board and cable mounting.