I just ripped up our runs to install a new (3/4") hardwood floor. After removing the rugs, I noticed 2 things I am not sure about. First, in one spot of the subfloor, there is a 1/2" gap between 2 of the sheets of plywood and one corner is maybe a 1/4" lower then the adjcent sheet. How do I prep this area?

Second, our pet (and the previous owners!) had some "accidents" in the room and you can see stains on the wood. How/should I treat the spot?

Thanks! Ian