Two things come to mind.
First (and this is the one you won't want to hear, so we'll get it right out of the way), you simply HAVE to have complete, current backups, unless you don't give a rodent's behind for what's on your machine. If your HDD thrashed itself while you watched helplessly, wouldn't it be nice to know that at least you've got a complete recovery (less a day or two's worth of work) sitting on your backup device? That way, regardless of the outcome, the DATA is still there waiting for you.
Second, document every step you take with Apple. Names, dates, receipts, conversations, results, etc. You have a lot more patience than I do (certainly more than 99% of the posters to the forum), but after eight attempts to correct faults, I think I would have already cheerfully suggested that they would save time - and money - by punting on the current machine, replacing it, and moving on. Talk to them as an equal, not a customer. Make business sense to them.
Don't let them lead the process. They'll keep trying to "fix" the problem until one of you gets tired of playing. Just explain rationally that this has gone to absurd levels, and you think it's time to just get this behind all of you.
Good luck, and keep us posted.
