I'm looking at the exterior carbon fiber kit for a 2.5, and it's listed at the same $9000 price as the 2.0. However, the 2.0 has a rear diffuser included. The rear diffuser sells for $1600 separately. Shouldn't the 2.5 exterior kit be priced more like $7500 then? Has anyone purchased the 2.5 exterior kit and brought this up?