ordinarily I would just drop the oil out and check it myself, but I don't want to touch it at risk of them trying to point the finger at me. However, I will insist that I be there when they pull it apart because they are just as likely to just clean everything up and replace the oil, even if the diff has half shat itself. Given the fact that I've done over 1000km with probably no/little diff oil, I'd say there's going to be damage. I paid for a new car so I want a new diff.