@DavidBlue If there are no holes or oil stains it is probably fine. If you tap it on a surface, debris should fall out, then blow compressed air on the backside and it should make plumes of dust until its all cleaned out. If it won't let air through to clean it out, replacement time. Honestly though, unless you have something in a rare size or that isn't made anymore, you can probably find a replacement cheap enough that the price would be worth less than the value of the labor used to clean it.