I mentioned in my last post that the Grammys have made a habit of giving the Metal Performance award to songs that were actually fairly old. That got me thinking. So I decided to research the issue. Here's the list of winning bands who won with a song that was significantly older, and the year of the award and year the song was originally released. If it was a cover song, I have noted that as well.
1991: Metallica "Stone Cold Crazy" (Queen cover 1974)
1996: Nine Inch Nails "Happiness in Slavery" (1992) NFM
2000: Black Sabbath "Iron Man" (1970)
2005: Motorhead "Whiplash" (Metallica cover 1983)
2010: Judas Priest "Dissident Aggressor" (1977)