Darn it! I didn't read any of the logs before I left (it seems the coordinates may be a little off); and I didn't take the spoiler pics with me. I was definitely in the right place, because I saw the item in image #1; but I really needed image #2 to identify the exact location.
A bit of a shame, because Smaug the Silver Dragon was eager to continue on his journey home. I will try again sometime.