Replacement o-rings are available at o'reilly auto parts (I just got em a few weeks back). Of course don't ask for our car specifically. I just pulled off one of the old o-rings around a bulb and asked them for a match. They brought up a big segmented box of o-rings and they had ones of the same size that work perfectly despite not having the flat spots where the bulb meets the lens housing.Wow major discovery for me today: the taillight lenses and bulb sockets. After 40 years, the likelihood of fumes getting past the lenses and then through the bulb sockets is huge. And the taillight gasket doesn't cover that area. The lenses normally screw down and seal right up to the housing. The bulb sockets twist into the housing with O rings, but over time both areas warp and develop leaks. I noticed slight warping in the lens mounting, and more importantly, looseness in the bulb sockets, after years of being seated in the same position and possible shrinking of the O rings. So, I have a solution. I can't find the O rings on the normal parts sources, I'll have to bring one around to local auto outlets and try to match. But whether you use new or old ones, try this: when you screw in the bulb socket into the housing clockwise, go all the way to the stop and then back off (go counter-clockwise) 1/8 to 1/4 inch or so, you'll feel it seat in much more snug and no rattling. Hope it's not doing anything bad, it seems so much more tight this way. It's just a suggestion, but now I know this area is a culprit. Pics coming. If/when I find replacement O rings I'll give a link. Sounds nit-picky, but whatever it takes to have Sister Golden Hair come sit herself back on down into that empty passenger seat.
They were however $2 each which surprised me.