I can confirm, the original SL cap has no "ears" and looks just like Jordan's.
There was a time when you could get a complete matching set of locks with a single key from SLS (ignition, doors trunk, gas cap...).
I was lucky enough to buy one of these some 15 years ago.
It wasn't cheap, though, but much more convenient than having three different keys (from P.O...)
I think it's NLA by now.
Anyways, I think the one key system was only on the 280SL...