Maybe a “dealer option” that would not have appeared on a build sheet? Every MB I’ve ever seen has had hirshman antennas unless they were aftermarket. The key for my manual antenna had a little paper hirshman sheet attached to it.

__________________
Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,