One reallocated sector is okay. You run into problems when that number starts growing quickly. Anything over 10 in my book is a cause for concern, but 1 isn't anything to worry about. Occasionally drives will simply have a bad block that can't be used. It happens.
I do notice that the start-stop counter exceeds the power-on time. You should try disabling HDD power saving so the drives don't spin down. If they're spinning up and down often, you may fry the motor and if they're spun down and you need to access something, it needs to spin back up again before anything can happen. A great example are my WD Blacks. They can take as long as 8 or 9 seconds to fully spin up to speed, so it only makes sense to keep them spinning as opposed to having to wait almost 10 seconds just to access the drives.