For seam splits try taking a thick piece of construction paper and cutting about 2" wide by 12" and folding it in half lengthwise. Then apply a light coating of Elmer's glue and carefully insert it inside the jacket and up tight into the seam. Be careful to not use too much glue and maybe some wax paper inside until it's dried. Not much you can do for the outer appearance, but you will have stopped the split from getting worse.