Oiled cards? Depends on how much your talking about here. If you dropped it in a pool of lotion yeah, let it sit for a month or chuck it. But talking about, doing several fans in a row and you get those one or two oily cards that cause gaps in the fan, the best thing would be just to remove the card that contain that oil. The oil's don't take that long to evaporate. You can also remove it manually, just get a clean piece of cloth and wipe the surface of the card.