The "controversy" about K&N filters and Mercedes engines is that there have
been cases of the engine MAF sensors being contaminated and requried
replacement due to the filter's oil. Most, if not all, of these problems
can be traced back an owner or shop using too much of the filter oil on the
filter, under the theory that "more is better."
Which leads to the question of managed risk. There is always the potential
for excess oil on the filter if not carefully applied and is there a
justification for that risk given the performance gain, if any? Another way
to look at it is . . . would you rather wear new underwear every 6 months,
throwing away the old, and getting a new pair. . . or wear the same
underwear for 6 months, send it to be cleaned, with the hope that you did it
right, then wear it for another 6 months?