I would like to know how to repair a zipper when some of the coils have become unsewn from the zipper tape; i.e., the thread/stitches have worn away from use. Do I just sew over and under the coils? The original stitches were like crochet, with the thread pulled through loops, and they went over the top of the coil as well the bottom. I don't have a crochet hook that small and am wondering what is the best way to proceed. The stitches must not get in the way of the "zipping" action. Any ideas?