I got real interested in crush washers the first time I rebuilt one of my brake calipers... they really do "crush" when you tighten
on them, and they've got tons of new ones down at the auto parts store...

Seems like the one on the drain bolt would work over and over... I never changed one on any of my dirt bikes,
and I changed the oil on them way more than necessary

... once when I was ordering some stuff
from HDL I got pack of about ten drain plug crush washers, now I change them every so often..
-Mike