I have a used, like new condition Challenge USA carbon rear diffuser. This is the less common, Sport version that is a bit more subtle than the race version they have on their site. Not sure if they still sell this version, but Greg from Challenge/GT Motoring can verify authenticity if necessary.
Needs to be re-taped and you'll be ready to install like a new piece.
$700 and ready to ship
Pics from GT Motoring:
Link to more pics: http://www.europeanautosource.com/pr...ffuser-e923-m3