It was on the second page of that post you posted
http://www.quiltingboard.com/vintage...ml#post5868213 <- points right to the pic
Also thought I'd mention, one of the stitch selectors pulls out to adjust, one pushes in to adjust. The front one is a push (left) , the rear one is a pull (right) . Sometimes if the front is on certain settings, the back one won't move. Try fiddling a little. If you've oiled in there, there's a good chance it's freeing up.