Re: crack within floor board
The best way would be to replace the split board. Get a new board the same or longer in length. Set your circular saw depth to just proud of the thickness and cut the split board down the center. Once this is done the grove side should be easy to remove, the other side you will no doubt have to pry loose and damage where the nails are through the tongue. Clean out all the debris and pull or cut off the nails. Cut the bottom lip off the grove side of the new piece of flooring, cut to proper length and slip into place. You will need to fasten it down through the top of the flooring with countersunk screws and plugs or countersunk nails and plus or fillers.
Be sure you live your life, because you are a long time dead.-Scottish Proverb