Although BRP specifies changing them at every oil change, you can often reuse them. Close inspection and proper installation are the keys. Look at the O-ring for dirt, tears, nicks or flattening, and check the fit to see that it is not stretched. Check the washer for nicks or indentations, and especially a large indentation from the drain plug. You can usually get away with turning it over and putting the drain plug indentation toward the engine one time. In time the copper washers work harden, and become less effective unless annealed, even if they are blemish free. I don't recommend using them indefinitely. One last caution, clean the O-ring and oil it lightly before you install it, so the cover won't grab, and tear or roll it.