I use to clean air filter of my Punto every 3000 kms by pressurized air. At around 8000 kms, I discard it and get a new air filter. Fiat service center owner advised me not to clean air filter this way as pressurized air will make filtering pores bigger. He told me to clean air filter by slapping it on some hard surface gently for getting the dirt off. Is there some point in his advice?