Have never seen MB headrests with one support either.

The headrest is almost identical to that one used by the Peugeot 604 in the mid '80s. I recall also that the 604's seat design tried to mimic the S-class seat design at that time.

Besides France, RHD countries were the most popular markets for the 604, so maybe someone decided to do the implant...

Just a guess...

A. Rosich
S320, 1998
E320T, 1995