I wouldn't call it stalking, more like hunting. Now, if you knew where the car was and sent the owner an email every month asking if they wanted to sell it yet - that would be more like stalking in my book.
If I were contacted by a previous owner who expressed an interest in buying the car back, as long as they weren't stalking with monthly contacts, I might appreciate it. I would definitely hang onto the info knowing that I would probably always have a quick sale and possibly for a few bucks more than I might otherwise get.
In this case it sounds like the car may have been getting parted out. That would be disappointing to hear...
Cal