I can add some info to this. My 1998 E300 had the original (black plastic) first generation SmartKey (the first year for this was 1998). When I bought the car the previous owner had the dealer provide a second key. This was the chrome and membrane button, round panic button style key.
When my son had the car, the chrome key went missing. So I went to the dealer and ordered him another key (for almost $400). They provided one of the newest style smart keys (with the discrete buttons and triangle panic button). It worked the first time we tried to start the car, but then the next time he went to use the car, it would open the doors but would not handshake with the anti-theft. The console displayed a red message regarding a key error. I connected my Xentry and the engine controller had a bunch of stored faults for DAS failure.
I called the dealer and they said, oh yeah, the newest smart keys don’t always work with those first generation switches. We will be happy to sell you a new switch $700 for the part plus over a thousand in labor to pull the dash apart and install it. And because it’s a Theft Relevant Part, we can’t sell it to you over the counter. And you’ll have to buy another $400 key, if you want 2 keys, because now your original black key won’t work with the new switch. Which all would cost more than the car was worth.
My solution was to buy a 2013 E350 BT, give my son the 2008 E320 BT, and sell the E300 to TimFreeh with only one functional key. Well I did give him the nice new shiny chrome key but warned him to never stick it in the switch.
So long story short, I am curious too how you managed to get your hands on a switch with the workshop key. I suspect that MBUSA would be very curious too.
http://www.startekinfo.com/StarTek/outside/153624/?requestedDocId=153624