I would expect the sludge and filings to be caused by the crunching and grinding. I expect that mine will probably reveal the same thing. I am taking it to the dealer Thursday to have them look over it. There seems to be a bit of oil around the diff sump plug, so perhaps there is a leak there and the oil level is low, either way I'm not very happy about it because it was at that same dealer not 2 weeks ago having the 1000km check done and I told them to check the diff because it was noisy, they just took it for a test drive (I rang them this afternoon to ask what they did - didn't even check the diff oil) and told me that "that was considered normal operation noise for this model." I'm not even a mechanic but if someone came to me and said their diff was noisy, the first thing I would check would be the oil. Seriously they must think people are fucking stupid. I've had a Nissan Silvia with a badly damaged and abused 2 way diff that made less noise than this thing. My girlfriend even asked me what that awful noise was, and she is normally completely oblivious to anything automotive.
We'll see how it pans out. If there is even the slightest hint of damage to the diff gears or clutch packs then I will be making them put in a new one. I paid for a new car, not a shitty half broken one.