No need to replace. The health percentage is based on the TBW, or total bytes written, which is chosen for warranty purposes. It does NOT relate to actual endurance.
In this case, the 250GB SL308 has a 75TB TBW. You have ~6.755TB written. There's probably more SMART data (scroll down, or check Hard Disk Sentinel) where it will list NAND writes vs. HOST writes - on my SL308 (similar drive) it's SMART values 234/EA & 241/F1. You're wondering why I mention this - it's because there's write amplification which means you do more writes than it states. In any case, based on your health % and wear leveling amount: (.82)(75) = 61.5, 75 - 61.5 = 13.5TB. This is exactly two times your listed host writes which could mean a write amplification...