Screw a PK screw in the hole in the top of the oiler and lever it out with nail pulling pliers etc or a slide hammer or even a stack of washers under the head of the screw as you tighten it down.
I've used screw extractors to good effect. A magnetic pick-up tool can be useful to make sure there isn't any broken spring in the hole. Any brass swarf might be a little more difficult, although tiny spoon ended dental picks can come to the rescue.