There isn't much to those sockets to go wrong outside of the brass clips actually fracturing. A couple things that MAY help - on the bulb, spread the bare wire leads away from the bulb base just a little bit. Also, on the flange of the socket, gently tweak the contact points up away from the flange a little. All of that helps make better contact with the bulb and contact pads. If the contact pads on the PC board are worn out, you can sometimes flow a thin layer of solder over them to get them working but that's a short-term fix. You'd really want a new PCB if that's the case.