For what the originals cost, is it really worth not changing it? I've seen a couple leak. Not many but if there's £40 worth of oil splashing around in there, do you really want to drop it again? Get the 2 washers and filter at the same time and you're sorted.
I think I paid something like 20p for the washers, at that price why not buy a supply so you dont have to take a trip to a ducati dealer next time you change the oil
I never knew you were meant to replace the washers. On the monster I just sold I did 3 oil changes and never changed them. Not a drop leaked from that.
At that price though I may start doing it just for the sake of it.