I have a 550i OEM diffuser that I purchased to be used with a Megan Racing Quad exhaust system. I had it all installed on Friday (5/24) and over the weekend decided it just wasn't for me. I had it removed on Monday (5/26) and it has been used for less than 100 miles. There is some slight wear to the exhaust opening from the exhaust rubbing against it during installation but it shouldn't be noticeable once installed.
Price is $80 including shipping via FedEx Ground to the continental US. Payment can be made by PayPal or cash if picked up in person in the Dallas/Fort Worth area.