Check under the lid of the first aid box. In my 190E the original child restraint anchor point for the centre seat position is covered by the high mount stop lamp. Due to this they have added a hinged extension which extends into the first aid box. Next to useless as it happens in my 190E as since it is a Sportline it has only two "bucket" style rear seats. I'm not sure if the same centre anchor exists in the W124 sedan as ours is a wagon. I'm pretty sure that in my father's '93 E320 coupe (124) that only two child restraint anchor points exist (on the shelf behind each head rest) since it, like my 190E Sportline has rear seating for only two.
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.