If you want to test a modern car for drain, consider Steve Brotherton's words in the thread below.
I hope the dealer solution works out for you. My gut feelings says this was not the problem. I hope I'm wrong.
Don't be surprised if the factory circuits test out OK. I'd bet on an after-market add-on..ie..alarm..ear-busting sound system, etc.
http://www.peachparts.com/shopforum/showthread.php?t=52492&highlight=negative+battery