I suspect that you may have an injector that is leaking badly. Trying pulling plugs one at a time and checking for a fowled plug. There is probably one plug that is sooty and black. That would be the injector that I might replace. The injector can drip after the vehicle is shutoff as the pressure is still in the system and as it leaks the fuel runs in to the oil by slipping by the rings on the pistons. However, it is leaking as well when the engine is running and should be causing the car to run rich and fowling a plug.