I think you'll find that Fuji will fix problems with SAB outside of warranty.
I bought a used X100 which looked like it was developing the problem, although it was very sporadic. The warranty was due to run out in mid September but I was away on holiday just before then and needed the camera. I emailed Fuji who said that any camera with SAB problems would be repaired regardless of the warranty.
When I got back from holiday I contacted them again and they sent me a pre-paid package to return the camera for a service. It came back about a week later with a sparkly, shiny new lens on it.
I wasn't even asked to send a copy of the purchase receipt although I did have this. I was REALLY impressed, especially as the issue only showed up very occasionally.
On this basis I think you'd be safe buying used