K&N has a good article on their website explaining how they have NEVER seen oil on a MAF sensor. Also, they go on to explain that the air speed thru the filter never really gets high enough to dislodge oil droplets, even from a grossly over-oiled filter. Interesting article; but of course it's THEIR article.

My friend installed one on his '02 320E. after a while the MAF failed. Installed a new MAF - again lasted about 6 months. We tore it down, found fine dust all over the intake tubing, and under a magnifying glass FOUND DRY DUST & TINY SCRATCHES ALL OVER THE THIN-FILM SENSOR ON THE MAF. Didn't find any oil though.
He installed the 3rd MAF, cleaned the intake and bought a new paper filter - no more issues yet, been about 2 years.

I run a cold-air oiled filter on my Vette, cause I want max power and don't drive it under any but the best conditions. I'll never put one in my Mercedes, to gain "maybe" 2 HP and lose the OEM air cleaning capabilities.

As a retired engineer, I appreciate technology and data; but to me, just holding a paper filter and an oiled-gauze filter up to a light an looking through them is enough evidence to convince that the gauze filter could not trap fine dust as well. Try it sometime - kinda scary.

DG