I have '08 Cooper S and need to replace the air filter but can't seem to locate it.

Can someone guide me where the air filter is located under the hood.

 

It is in the long rounded type plastic piece that is closest to the windshield. If you follow the tubes that go to the turbo it will lead you right to it.

 

It will require 2 different size Torx drivers to remove the cover. One size for the 4 screws along the front edge of the cover and a larger size for the 2 screws that attach the turbo tube and MAF sensor to the front of the cover (sorry I don't remember the exact sizes).