Forgive me for not being as knowledgable about the E420, but didn't the years 94 and 95 W124's E420 get the "ECO JUNK" wiring, that also affected the Throttle Actuator?
With the E320's, it is very common to have ECO wiring, starting from the Throttle Actuator, to blow up some vital modules, if not soon replaced. I can only speak for the E320's, what happens is that the wiring insulation returns to powder. To make it more difficult, you can not see the now blank wires, since they are hidden inside a sheath. Once you cut that sheat open, you might be getting close to a heart attack.
Again, I don't know for sure if this was a problem with the E420's of that model year.
The symptoms seem to be the same as with the E320's. Usually stall's after applying some throttle, etc.
Now, if this is so and the Throttle Actuator wiring is bad, than the dealership knows exactly what happens if driven in this condition. Chances are that your CC/ISC computer goes, or already has gone out, along with some other directly involved modules. Meaning, more mula for repairs to be done!

You are absolutely correct--The 1994 E420 had the same problem engine wiring harness as well as bad wiring inside the ETA. I had presumed that his harness was okay, but if it is in fact original, there is no sense replacing anything else before replacing the engine wiring harness first, then check the codes and see what you have.

The ETA is incredibly expensive to buy from the dealer. Your best bet is to search ebay for an ETA with a date tag after 1996. The newer ETA's didn't have the same problem. If you get lucky, you may find one for about $300.

There is a great wiki over at the ********* on determining the date of your ETA