CR's went down on Benz products as well, at least the ones that came to the US. The US equipped cars had to pass the same tests, and at that time, MB had no magic solutions either. I'm trying to remember if my wife's '73 250 had an EGR valve, I don't remember one, but it was a US model and must have passed emissions testing somehow.

The valve situation was the same. In order to hold up for long periods with unleaded fuel the seats had to be hardened. When the catalytic converters came along in '75, the hardened seats came with them. I have a '78 Ford 4X4 pickup that was just big enough that it did not have to have a catalyitic converter, but it got the hardened seats anyway.

Have a great day,
Larry