Originally Posted by Chris L.
If they don't crush what benefit would there be to using a new one every time you change the oil?
Brad, are yours OEM?
When tightened the soft copper/aluminum is crushed into the surface irregularities and seals the face joint, using it again means it has the old impressions in its surface and could leak through them. It is also harder because of the surface has been work hardened. It still might work but not as well as the first use. this would also apply to the crushable types like the old spark plug washers.