We covered this subject a while ago, and having discovered that the air filter is the same as the Series 1 Roadster, I had intended to change the filter for the 'as new' Roadster standard filter, then get a K&N in another year or so. But I've changed my mind!
Here's the original:
New K&N:
Detail of part number:
It slots in easily............
And back in the car.
I also bought a service kit - cleaner and oil, so when I do the Roadster service later in the year I can spruce the filter up.
