that portion is just for show. if the bottom fram, the thicker wood, were cracked then you might want to look into it furter, but for that I think you're ok.
If the tank is old and you have any concerns about it, IMO
, I'd do it just to be sure. There are articles around (I think even one in this DIY
forum) that walk you through resealing a tank. It's not that tough.