You can use a light bleach mix if the owner doesn't mind. Most of the ones I have cleaned I used BT200 because it's a green product and the customers did not want me using bleach. It works great, just requires a little more time and effort than bleach. BT200 is an oil stain grease remover but is also great for Mold and Mildew.
http://www.eatoils.com/product.php?id=62
http://www.eatoils.com/product.php?id=62