I'm not sure in all cases but a few months ago, I replaced the tank in a 87 SDL with one from a 83 380SEL. It fit fine. I did change the tank screen because the one in the SDL was a little different inside the tank but the same outside. They both had the same lines, all the same size and was no problem at all.

EDIT: Oh, I did have to remove the tank restricter from the 83 tank but that wasn't a big deal.

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84 500 SEL (307,xxx miles)