Hi,
Yesterday I drained the front diff on my '95' and found a layer of fine silver paste on the magnet - I would consider this normal for a car with 124,000 miles.
When you say 'swarf', do you mean actual spiky bits of metal or, like me, do you have what looks like the scrapings from the bottom of an old silver paint tin ??
If you have real shards I would suspect a problem.
Bob.