My X-T1 came back from Fuji Support... again they turned it around in a week! - That's 7 days from first reporting the issue on their website to receiving the camera back repaired.
I took extra care to describe the issue on this occasion and included some example shots on a memory card. Fuji Technicians replaced the sensor and having taken some test shots I can report that it is now spotless.
Well done Fuji