Originally Posted by Z K
Using an oiled air filter on the E9x M3 doesn't make a difference as it uses a MAP sensor. There is no MAF sensor to foul. I would never use a oiled filter on an MAF equipped car.
Oiled is fine on HFM-equipped models (e46M3), as long as its not overoiled, which many people tend to do.
E9X M3, no issues at all.