Has Seagate changed their warranty terms? Last I knew, they honored the warranty on the drive, not the enclosure...so even if you took it out of the enclosure, you could still send it in for warranty.
Some drives I removed from enclosures back to the 7200.12 and first gen Cuda XT's (up to 3TB) had SN's on the drives you could warranty check online. Most Cuda XT's that are 3TB (CC45 firmware and newer) don't clear the warranty checker with the SN on the drive, only the SN on the enclosure (which is 1 year.)
Seagate is intentionally selling drives that will self destruct in external enclosures with 1 year warranties. The ONLY drives from manufactures now that don't park themselves to death are NAS\DVR drives or some "performance" drives like Hitachi 7K4000 and WD Black. From what I've seen all Seagate drives have APM set at least 128 now, causing head parking. This will destroy a drive if you use it for seeding torrents and constant access.
I miss (the old) Hitachi. It's well documented their Deskstar and Ultrastar drives had the highest long-term reliability. Their 5900RPM drives had higher sustained IO performance than most competing 7200RPM drives!