My zig-zag won't zig or zag )-:?

I have a Kenmore #158-13571 that is about 32 years old. It has always worked perfectly until a couple of days ago when the wheel would get really hard to turn and almost lock up for no apparent reason in the middle of stitching a seam. It felt like it does when the bobbin thread gets all tangled up on the bottom of the fabric, but that wasn't the problem. I oiled the machine for the first time ever (without touching any of the inside parts with my fingers or the oil can), and now the machine runs like lightning, but only in a straight line. It won't zig-zag or do any of the other 10 variations of zig-zag type stitching. It might be that whatever inside the machine that moves the needle left and right when stitching does not engage when I turn the dial on top of the machine to select the stitch that I want to use. I say this because when I turn the knob that controls the width of a zig-zag stitch (without the machine running), the needle does move from left to right over the presser foot slot, so I know that the needle is not stuck in place. I'm relatively handy...any suggestions? Thanks. Marilyn