Backup your data and do a secure erase https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase
or just use http://partedmagic.com/
The sleep backdoor described in wiki article is functional with parted magic also.
Regularly backing up your data is always good practice. In the overall big picture 13 sectors is not alot as you can see the available reserve space is still sitting at 99%. Your SMART data looks fine. I don't think you have a problem.