I recently decided that I would replace the cabin air filter in my 2006 WRX. I got it a couple months ago and wasn't sure when it was changed last. I bought the cabin air filter off ebay for about $10. It was a very simple job; it took about 10 minutes. There are 13 screws you will need to remove. Twelve of them are in or around the glove box and one is a plastic fitting on the right side where the door mates against the side panel. It is a pretty simple job. Remove the plug shown in the third picture. Remove the twelve screws in/around the glove box and the plastic fitting on the right side. Remove the lip that covers the filter housing. Pull from the bottom to avoid breaking the clips. Carefully remove the old cabin air filter and replace with the new one. Then, reinstall !