5 speed Auto Trans fluid drain plug O-Ring or aluminum washer?

For the 2008 Saab 9-3 5 speed automatic transmission fluid change the drain plug lists an O-Ring #90348863 and not an 18mm aluminum washer. I can't find an aluminum washer listed with any of the 2008 9-3 parts. Was there a change in the transmission in 2006 or does it matter? The illustrations for the transmission fluid change for the 9-5 and 9-3 shows an aluminum washer.

Any alu washer of any brand from the correct size is okay don't worried

eSaabParts says the part number for the 5 speed automatic transmission drain plug washer (o-ring) is 90348710, which is aluminum (18x24x1.5mm) and it looks like it is for all Saab models with the 5 speed automatic transmission.