I just bought a 94 Chevy Corsica 3.1 from a friend. He put a K&N drop-in filter about 2 years ago/30k miles ago. He's never taken it out or anything, so I was wondering how they are supposed to be cleaned? As far as I know, they pretty much last the life-time of the car, as long as you clean them regularly. I seem to remember seeing some kind of cleaning spray at Auto Zone, but I'm not positive. Anyone know for sure?