So my external Seagate drive is no longer seen by FCPX. It was there, the Events all loaded and then they just one by one disappeared and then the drive itself. This happens whether it's hooked up TB, FW800 or USB. Motion sees it. Compressor sees it. PPro sees it. After Effects sees it. Tricky little bastard even iMovie sees it.
So it turns out it was because of a Hasselblad DCIM folder I had copied on to the drive after a photo shoot the other day. FCPX saw it and said, "That's a camera. I don't care what kind of Events you have. That's a camera." And yes, the drive would show up on the Camera Import list, but only with the first folder that held video clips available. No ability to look at or reference any other folders on the drive. I took this to be just another bug. And I suppose it is.