I have a liberty sport v6 and all of the sudden I am getting awful gas mileage. I just recently changed the oil and plugs. I thought it might be the air filter so I went to change it. The 1 that was on it wasn't that bad but I noticed a sponge in the side of the box. It was covered in an oil like substance. The parts guy at the dealership told me to rinse it in gas, yeah, it decinigraded. They don't show it at the dealership but I know it needs to be replaced now since there isn't one there at all. How and/or where can I get another one? and what is it called?