I had a similar issue on my wifes Seat Alhambra.
its a 2015 and after pulling the adblue injector / out of the exhaust end, it was all caked up and crusted up. We fixed that and a few weeks later it done the same thing.
Being a little bit older and not really "needing adblue" i spoke to a very knowledgeable mechanic or 2 and their advise was "get shot of it, just map it out and the car wont ever look for it again" so thats the option we went with. the car has been thru the NCT since then and there was absolutely no issue with emmisions tests etc