Keyhole, you were right on the target. Benz dealer told me ETS control module is bad on this car and it would cost $1002 to replace it. Cost of the module is $825.
Jeez.... that's a big financial jump from simply replacing your brake light switch...
I can attach some technical info about the location and function of your ESP control unit - but unfortunately my WIS does not give the information on how to remove it. It looks quite obvious, and is easy to access in the engine bay.
However, as I see it, you are over a barrel here with MB as they have advised replacement of an expensive electronic module, which they will not accept in return if you
fit it - and it is not the real fault. That non-return policy for modules seems to be common. We have it also in the UK.
In your shoes, for peace of mind I guess that I would (reluctantly) let MB take it from here on. If they change the module and it does not fix the problem, you will not be out of pocket. If you did source a cheaper N47/5, would it have a warranty? Also, (although not stated in my WIS, as there is no procedure) on other module change-outs described in my WIS, there is always the requirement to hook up to the MB STAR diagnostic system before the job is completed. So probably you would have to hand it over to MB after your own work, anyway.
As you will see, it is clamped directly to the Traction control hydraulic unit (A7/5) - the item with 6 hydraulic lines attached. Maybe the N47/5 cover has to be removed first to show the bolts that are holding it to A7/5.
Let us know how it all works out