Great forum & thread. Came back to airport last night after 10 days and 30 minutes into journey home, the aforementioned brake servo restricted msg appeared on my 2019 A6 40 Tdi. Like many here I was ‘comforted’ by the “continue driving” text. Curious got that I am though, I thought I’d google a little his morning knowing that however minor, a trip to the dealer was going to leave me short a few hundred at best. Thanks to the good people on here, the car is now parked up, a spurious sensor ordered from eBay at a quarter the cost of Audi and a video tutorial on how to replace. I’ll post again in due course to update on the quality of the part from eBay. Thanks all! Frankie