It seems to me we should have a gasket between the car body and the tail light housing. I don't recall ever having any leeks, though it just seems wrong!
I have the one between the housing and lens and am quite sure I've never seen one at the tail light housing to car body , but am I missing something?

Try 914Rubber. . he's got almost everything for the rubber parts. . AA has them. . all they are is a form rubber gasket. . you can make your own using foam weatherstripping from Home Depot.. put the join in the middle of the lower edge. .

Mikey's kits are perfect !!!! IMO

I have the foam rubber one from Mark though I thought that was between the housing and the lens, am I mistaken? If so is no gasket at the lens? Thanks I guess Im getten old!

There are both. The one between the lens and housing it a chord that seats in the lens. The body to housing is the closed cell foam. Mine have a self adhesive back that allows you to stick it to the housing and install as one piece. I did initially make them without, but after finding water in my trunk I took it out and noticed it had foled over in the corner. I was careful to install it, and figured this was a needed improvement.

Hope this helps

I finally decided that the easiest and best seal was a thin strip of butyl rope like that used to install windows. It seals well, never hardens, and is removable when needed.