The car should not die! You have a couple of alternatives:
You are right, the BMW part 34316754048 seems to be out of stock everywhere. The alternative is to buy some copy, most probalbly made in China.
But I would go for a renovation kit and use some brake shop for a renovation. It is simply made. If it is no rust in the cylinder you can change all the gaskets easy. If it is rust, a professional shop will renovate it definitely in less than an hour.
In the old days, you always made renovations of the cylinder instead of buying a new.
Or find a used one. Search on the part number! It must be used in a lot of cars.
I found one link that seems to have it:
https://www.original-autoparts.com/prod ... a560f35e98