First, the sealing washer you are referring to is not a crush washer. You can never re-use a true crush washer as they are permanently deformed from the original install.
I sell seal kits so telling the truth here may cost me. But you can certainly reuse the copper washer on your final drive, and every other drain plug. This goes for the O-Rings as well. I have proven this to myself many times. I do recommend, as a minimum if you choose to go this route, having an appropriate seal kit on hand in the event that you find a damaged seal. Otherwise, you risk down time waiting for a very inexpensive seal to arrive. It may not be available at your local dealership or parts store.
I am not saying that it isn't a good idea to change seals when servicing your machine. Seal kits are very inexpensive insurance. Just saying that unless you see visual damage or, in the case of an O-Ring, feel a nick, cut or deterioration, my experience is that you're good to go. Especially in a zero pressure environment like the final drive on your Ryker.
