after speaking to bosch and going on a pierburg technical training course.....i can safely say i will never use a k+n filter ever ever again.
they had problems with A mas sensors failing on all sorts of cars and concluded after much research that the specific problem with 99% of all failures was down to the oil used in k+n filters, as soon as you stick your foot down it sucks the oil through the filter and into the engine causing many problems.
that said..
all filters are not the same,
use ADL (blueprint) or Mann and Hummel wich carry block exemption (covers manufacturers warrenty if fitted aftermarket) wich no other filter company can offer.
and no when i get a filter from andrew page at 48p thats cost plus 10%, at halfords that was supposed to be a decent staff rate (15%) wich is a joke.