Hey Warden, Call A-Crane in Redwood City if you want keyblanks or have them cut a copy, that is where Autobahn send customers wanting key or lock work.
Most locksmiths have a hard time with the Mercedes blanks, and will not (can not) make the new electronic keys.
My brother is a locksmith and explained to me that it is common to have to make several attempts to get it right.

And the brass material in the aftermarket blanks wears fast, just look at the dust that comes out of the starter switch/key hole.

Keys are the one thing I recommend only the dealer for. Code-cut keys use a nickel alloy that lasts much longer.
I just got a code-cut key for my '71 220, only $22. They still have the codes on file and it fit perfectly!
You can order the master or valet key.
Dieseldiehard
1971 220 (gas) 4-spd manual 104041
1979 300TD w/ ’85 turbo engine 289560
1983 300D 237490
1985 300TD 206150
1975 300D (looking for an engine)