In performing the my first oil change on my new to me xr650r it appears that the small round o-ring in the area of the long cover bolt is missing. Also, the diagram in the owner's manual apparently shows a dowel at this location? I completed the oil change without replacing the small round o-ring and dowel. How critical is this? The o-ring that follows the perimeter of the filter cover is in good condition and there are no leaks.