The recommendation is to leave it alone. Autumn Blaze maples are very susceptible to bark splitting. It is a weakness in their character. We no longer recommend the use of sealants such as pruning paint or tar. These products actual inhibit the "healing" of the crack. Notice at the edges of the cracked open area a roll of tissue called callus tissue. This growth, given enough time, will grow over the exposed wood. If one paints the exposed wood, it will interfere with the growth of the callus material and slow the "healing" process. Other recommendations to go along with this are: don't pile mulch up against the trunk of the tree; don't get soil up against the exposed wood (you want that wood to remain dry); keep weed whackers away from the bark of the tree; and don't use Roundup around the bases of thin barked trees like young maple trees.