There should be two screws holding the light plate on, under that is the bracket holding the needle bar. There are pivot points on which this bracket turns to move the needle bar to zig zag. Oil or heat these pivot points. There is also a rod connecting this bracket to the gearing underneath the curved piece on the top of the machine. When you move the ZZ stitch width lever you should see another bar slide in the curved piece; that whole curved piece swings back and forth when the machine is cycled and the rod connecting to the needle bar swings with it. Oil or heat under and around this area. By "heat" I mean either a hair dryer or a heat gun. Because you've already oiled you could start to smoke that oil, so be careful and don't use heat where there's a smoke detector.