While cleaning and painting the shift lever / shift bar I noticed that years ago I had tweaked the design to reduce play in the shift lever. There was excess movement in the lever to bar junction. Your situation may be different.
Two thin washers can be added on each side of the shift lever tang (inside the fork of the bar) to take up the play when the shoulder bolt is torqued. I ended up using .030” washers. Thin washers are available in various thicknesses from several online sources. Grease all the contact surfaces.
Test to be sure that the lever moves freely when the shoulder bolt is torqued. The stack of washers and shift lever tang should be set slightly less than the thickness of the tang plus the one side of the bar fork.