why is my airfilter ful of oil ?

BLLOWWWW BYYYY!... Sorry to say, Combustion is getting past the rings. You can try to help it by making sure the PCV system is working at its best but anything short of a rebuild isn't gonna do much.
Make sure the VC baffle isn't clogged up with sludge or deposits. If the oil can't drain back fast enough the vacuum on deceleration can pull the oil out from the baffled area of the VC & it ends up in the air cleaner.