I have a brand new Subaru OEM rear aero diffuser with the mounting bracket and all hardware for sale. This was a factory installed piece on the 06-07 STi's but can be modified to fit the earlier WRX or STi's. It will also bolt up directly if you have the Cusco rear subframe brace. I intended to install it on my '05, but I sold the car before I got around to it.
I will take $75 shipped, or $60 picked up. PM me for pics or more info. I will accept PayPal.
Phil