It will contaminate the MAF if you oil the wrong side or over oil the filter. Many people like to blame a product for their own stupidity. Besides that, Mercedes MAF's are known to be pretty much crap and will fail around 40,000 to 50,000 miles regardless. I have been a K&N user for over 10 years and have had no issues in any of my cars. At the very least, it is nice to keep the old filters out of the landfills.