If I were you I'd take a Dremel tool with a pencil-diameter-sized cylindrical sander and route a channel down that crack. Taper the channel a bit with a sander, lay down some thin strips of fiberglass and thickened epoxy, sand it smooth, paint it, and see what happens next season. Maybe a two-hour job, not counting cure time. The longer those cracks are submerged, the more water will seep in, the larger the cracks will get, etc.