I know where you are coming from, I do. I would be exactly the same.
You paid good money and you want everything to be perfect. It is completely understandable.
There are 100's of sensors on all modern cars and the law of averages suggests that you might just get one sensor that's not all it should be.
The irony is that the sensor that has failed could be the same sensor fitted to diesel super mini from another brand.
Lots of components are shipped under different labeling for several makes, so you premium vehicle (And it is a superb vehicle right?? - You know that - We all know that - That's why we are here
) could well have a few components that are interchangeable with some not so premium ones for sure.
I really hope that is the case for both of you. Hopefully a single trip to the dealer and an hour later it could be the last time it sees the dealer until your next service.
Try not to get into the mindset that the Cali you have is a lemon and will be constant trouble to you. It doesn't necessarily have to be that way. We have the warranty to give you the peace of mind that VW sort these things out either today, or years down the line.
I spent ages on here waiting for the Cali to be delivered. By the time it was here I had convinced myself that I would have a van with just about all the faults that have been discussed on here. I had a list of issues that recent recipients had posted about. The lead time for deliveries does nothing for the paranoia does it?
Sounds like your sensor issues are T6.1 related rather than California related, so its far easier to find a dealer that can sort an exhaust sensor, rather than one that knows Cali's and cant work out why your roof sags or your waste water leaks back into the van.
Fingers crossed for a speedy resolution and many enjoyable trips ahead.