equus77 saidThanks. I did take it to an Apple certified store and they did confirm that it was the drive. Fortunately I don't think I've lost too much that is important. Most of the pics I want to save are on my phone or can be transferred via Time Machine. It's just a pain to reload everything.
Interesting thought - I don't myself know if the thousands of pic files I have on my iPhone and iPad are at the same full resolution as I have in my iMac, or if they're reduced. A quick check tells me the iPhone photos take 13 GB of storage, but I've never tried to download a pic from the iPhone, so I could compare with the original stored on the iMac.
So I just now did that, and the iPhoto original is 1.8 MB, whereas the iPhone download of the same pic is smaller at 1.2 MP. BUT, the iPhoto original had been cropped, and iPhoto keeps the cropped-out part, even though you won't see it until you crop again. Apparently iPhoto exports only the cropped image, though, and that's what gets synced to iPhone and iPad, the smaller cropped version.
So, if your iPhone has images you edited in iPhoto, you'll only have the final pic, not the full original that iPhoto retains. But at least the resolution is preserved in the iPhone, so that's good. And pics you haven't edited will be the same file size in the iPhone as your MBP had.