I have recently rented the large drum sander and tripped my hardwood floors of the top finishes. I ran into a slight problem though. There are significantly dark stains in the high traffic areas of the floor. I tried to sand down below them but I am afraid of sanding too much and having a noticeable dip in the floor. I am wondering I guess if there are any types of cleaners I can possibly use to pull the stains out or I am just going to have to try to sand below them before refinishing?