It is quite possible that the copper washer is missing, or has never been replaced. The washer should be replaced at each oil change (when using the drain method). There are normally an assortment of washers with the filter, the copper is for the drain plug, the aluminum is for the filter bolt and the other(s) are for different applications.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.