Is there a reason why Volvo wants you to use aluminum oil pan plug washer and not a copper one?

John 2007 v50

 

They want you to use the aluminum one because over time using the copper one it will crack the drain plug. It will crack where the head meets the washer.

 

Personally I believe the aluminum oil plug washer seals better then copper, but they both do a good job. You should always replace the washer after each oil change. I have seen many times where the washer was left off creating a small drip. Owner does not see the oil hitting the ground because the engine cover catches it.