I cannot say for sure if the 124 has one, but I can't think why it wouldn't. It would be toward the top of the box, probably on the inboard side. Looks just like a brake bleeder, maybe larger.
Plus. if this is on the 500, it will be a tight fit to see or access the bleeder. I'd check the TE first
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.