Did the reallocated sector count change after the scan? If it did, continue scanning, running Seatools, or creating or deleting large files in the free space to exercise the drive periodically. The count should stabilize or hasten drive failure. Also, Hitachi's
Drive Fitness Test diagnostic has an exerciser that will work with any drive and will run for a user specified amount of time; good for new drive burn-in. The
Seagate Community Forums : Reallocated Sector Count increasing (ST31500341AS ) discussion may be of interest.