A good bath will help narrow things down. Oil in the air filter is normal on these fine cars and there is a separator and a drain that returns it to the pan. There is a revised flat baffled breather hose that goes from the valve cover to the air filter that cuts down on drips. The other common sources are the valve cover gasket, the turbo drain line seals the air filter drain line o-ring at the pan. the oil filter housing to block gasket. the IP to block gasket, and the front crank seal. Start at the top and work your way down.

Bob D.