Watching A Hard Drive Slowly Die

I suppose I should have a better idea about what's going on, but I'm stumped, and I'm pretty sure I'm watching it die.

I've got this 3 TB USB drive that's served me well for a few years. It's housed my media collection, it's served as the data source for my Plex server, it's made me happy by giving me a little blue light that lets me know I'm not alone in my home office. Lately, though, it's stopped behaving in a reliable manner. Out of the blue it will unmount, sometimes it will still show as an attached device but remain unreadable, but removing and reattaching (or just rebooting the computer) fixes the problem for a couple of days. Recently I got ambitious and ran chkdsk which found, and repaired, a couple of errors. Things were fine for a bit longer, but eventually the problems came back. Some of the behaviors seemed to be acting like file locks, so I shut off the indexing service (this feature has gotten better in the last few years, but the value it provides doesn't outweigh the problems). Things again got better for a few days, but then I got a completely new problem. My drive was partially available. Some directories read with no problem, others presented a cyclic redundancy error. Ok, chckdsk...but no, that won't work because chkdsk suddenly thinks my drive is a RAW filesystem. Windows still reports NTFS, and I can still browse significant parts of the drive, but chkdsk is still confused. Another tool claims there's no partition. Liar. Lying Bastard Liar. Thinking the end was finally at hand, I tried my last ditch Windows effort: when all else fails, reboot. So I rebooted. My drive mounts, Windows detects errors, offers to fix, fix, and I'm up and running again. 

I really don't know what to think about this whole thing. I've lost hard drives before. I've lost them out of the blue, one day good, next day no more. I've lost them over time, reads get slower, odd noises come out of it, eventually no more. This is a little different. This is behaving more like there's a process somewhere that is forcing an unsafe unmount of the drive, and when I go through a remount or reboot the drive behaves as if nothing at all is wrong. This is the part that's confusing me. Sure, it's probably dying, but it's dying in a way that I've never seen before. 

Oh, well. Death of the drive is nothing more than an inconvenience. My backups are running, my backups are good, I've just verified that my backups are up to date, and with that fiber connection restoring to a replacement disk won't take all that long.