There were no post war MBs that required leaded gas as they all had hardened valve seats.
The problem with leaded gas had nothing to do with its toxicity the stuff they are using now is supposedly a lot worse. The problem with lead is what it does to the inside of a catalytic converter. On the atom level it bonds with the platinum defeating its activity as a catalyst. The amount on the surface probably could only be seen with an electron microscope as only a few atoms thick totally kills the catalytic action.
So, whether it is legal for some use, it is ABSOLUTELY NOT legal to add to any car in the US that has a catalytic convertor.
Bosch Master, ASE Master, L1
33 years MB technician