I think Skywagon mentioned in another post he had a problem with MAF sensor after using K&N filter in his VW, so it may be car specific, but I can't see oil deposits to be good on this type of sensor, especially problematic after re-oiling the filter by the user (factory could be more consistent with the amount of oil spread inside). Also, unless the area is extremely dusty , you could probably run the car without any filter as well. As a mater of fact on my old Nissan the duct going to the engine intake cracked on the bottom and was sucking unfiltered air probably for few years before I noticed it, the engine run well all the way to the very end of the car's life of about 270k miles , when I didn't feel spending thousands on broken transmission and junked the car.