As I said, they were used, so I knew that a drive breaking was kind of an inevitability. As far as I'm aware there's no warranty, I certainly didn't pay for an extended one.
Good news though, since writing this I just started playing with dmesg and smartctl, it actually might be something with the SATA connector. At least those are still pretty cheap.
It makes sense, at the time you bought them there was no supply crunch plus being run in RAID. Would have been a decent deal.
Nowadays I feel like an underworld scrap goblin, all the old PVRs from family and friends are being cracked open for the HDDs. Time to slink off to my cave of spinning platters.