I'd try an electrical contact anti-corrosion product on every bulb first.
I use Corrosion X, and put a drop or so on a Q-tip, then coat all of the areas in both the receptacle and the bulb where either + or - connection will be made. Once treated, with this, I've never had another problem with transfer of current from a receptacle to a bulb or any other contact surface (e.g. fuses, etc.). I have a friend who had an ocean going sailboat and a few years ago, at dusk, the light on the mast would not light (and he had no spare bulb). He climbed the mast, treated the bulb contacts with Corrosion X and put the bulb back. Within a few minutes, the bulb lit, and stayed lit whenever turned on for the next year or so.
Whenever I do anything with electrical contact surfaces on an older car (5-6 years or more from new), I follow the procedure above. It is a wonderful corrosion inhibitor. Corrosion Block seems to provide equivalent corrosion inhibition.
Gary