Engine coolant drain plug gasket?
 

I recently changed the radiador, water pump, and hoses on my 82 300d Turbo. When I drained the block, I did not notice a copper washer on the drain plug. Since it is designed exactly like the oil drain plug except that it is larger, and due to the fact that it is leaking slightly, I assume it is supposed to have one. I cannot find one on fast lane, or other parts suppliers on the web. Since I have fresh MB orange in the cooling system, I would rather have the washer in hand when I pull the plug again. Does anyone know the size of the washer if there is one, or where I can find one. Thanks.