There is a steel line that comes out of the wastegate and slides into that hole in the compressor housing.Its purpose is to keep oil from building up in the wastegate,It simply bleeds off some boost and that is what pushes the oil out through the line then into the compressor housing inlet.The oil comes from the engines crankcase vent that dumps oil into the turbo inlet.
If you can't find this line you could just plug the hole in the compressor housing and leave the wastegates small orfice/bleed open to atmosphere.It may make an oil mess thats all.If you plug the bleed also then boost pressure will be lowered due to the wastegate opening a little sooner mabye 9-10 psi instead of 11-12.