I had a similar bad run with Seagate 3TB drives..3 out of 4 in 2 years. I was really thinking it was the NAS, but switched to WD Reds and have had no issues in 18 months.
That isn't to say that reds/greens don't have issues... I've seen one of each fail, but they have been very solid compared to my experience with Seagate drives... the shame is that may very well be different today, but brand (dis)loyalty tends to carry for longer terms.
