V'gal:
It is more likely that a bulb is loose in the socket, or the socket has deteriorated so that it makes intermittant contact. Take out the bulb holders and bend the tabs in a little, smear a little dielectric grease on the tabs and reinstall..if that doesn't work,see if you can get a new wire circuit board for the tail lights (if you have a sedan). Wagon, you gotta get the whole lens.
buena suerte,
el Raidman