If it's 12' that's probably an Oday Widgeon. The Oday "Daysailer" was 16'. Both great boats. I learned to sail on a Widgeon. The one thing to be aware of is that most of the early Widgeons were not self rescuing. They wouldn't sink if they tipped over but you needed some help from another boat to bail them out or pull them to a beach.
The fix is easy. Buy 9 feet (or three times the length of the crack) of 4" wide fiberglass
tape, a quart of epoxy
resin, and the appropriate amount of hardener for the epoxy. With masking tape on the inside of the boat, mask an an area that is 4" wide around the track and slightly longer than the crack. Sand the area then clean it well with paint
thinner or other solvent. Mix the resin (follow directions, mix well) and brush it on the boat with a cheap
paintbrush. Lay on a strip of fiberglass
tape. With a gloved hand press and smooth the tape well into the resin. Brush on more resin to completely fill the weave of the tape. Lay on another strip. Brush on resin. Lay on another strip. Brush on resin. After the resin starts to harden, pull off the masking tape.
After it hardens you can sand it and/or paint
it for looks - or just leave it be.