Here I propose to collect a list of verified companies which can reliably diagnose and fix various components on our precious cars.
I've inquired Bosch directly regarding the ECU and ABS module of my Q4, and here's the response I got:
The Bosch Repair Service is offering a repair service for ECUs. At present both part numbers, 0 261 203 301 and 0 261 203 834, are not in their assortment. But usually they are still able to check/repair ECUs of the Motronic (but it might take longer than usual). If you are an end customer feel free to ship us the ECU as the Bosch Repair Service is for workshops only:
Robert Bosch GmbH
Automotive Tradition (AA/ATR)
Auf der Breit 4
We will then forward your ECU to the Bosch Repair Service and keep you informed about the progress.
Bad news about the ABS2. At present we are not able to help you out. The Bosch Repair Service sees the need of the market and is already checking the possibilities of repair solutions here. But this will take lots of time.
As you can see, there is some light at the end of the tunnel.
My point is to have a verified list, in a similar way we have one for alternative parts. I think we should also push the vendors a little bit, especially regarding those rare parts, like the ABS2 for Q4 and Viscomatic.