A more cynical view would have it Mercedes sound systems in any cool old car you find will not be very advabced and it comes to a shock to our younger friends who were born in a world of MP3 players and bluetooth earrings but some radios in cars that had chrome, not plastic, body parts were surprising primative. You turn the radio on, turn a dial and you could get AM radio out of a single scratchy speaker in the front. Some cars had two speakers in the front and some had FM whole others had FM stero or speakers in the back, too.

Mercedes invariably installed a front/rear fader for the speakers. These usually suck badly after a decade or two.

The speakers are a weird euro size in many cases and won't be the size you find in your store (unless you live in a weird Euro country).

Becker, linked from this page is the nest source od dealing with repair of old stuff or sepeakers in wierd Euro sizes.