Now I'm really confused! People I regard as the leading experts on 113's -- Bob Geco, Pete Lesler, and Gernold Nisius -- differ as to whether the thin gaskets were on the 230SL.
My 1965 230SL, which was quite original when I got it, has the thin gasket only behind the trunk lock chrome. However, that doesn't really prove anything, as it had been painted once. As another data point, the Mercedes Classic Center in Stuttgart currently has a beautifully restored 230SL which has them behind the taillights but not behind the long chrome strips.
It does seem like a good idea to have the gaskets behind the taillights, to keep the chrome from touching the body -- even if Mercedes didn't think of that originally (which seems unlikely). However, I don't see any need for them behind the long chrome strips, except possibly cosmetic.
Chris Earnest