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The best website for information on fixing your Mac iFixIt.com
(view it here
). There you'll find manuals for just about every Mac, instructions on how to replace parts, and the ability to purchase common components.
I would never recommend purchasing rebuilt or used hard drives. You'll never know quite what you get, and your personal information is not something you want to mess with. Plus, the prices have become very reasonable as of late, so it's always worth it to purchase a new hard drive.
The nice thing about hard drives, is that they're universal. You simply need to purchase a 3.5" SATA hard drive, from anywhere, and it will work with your Mac.
Let me know if that doesn't solve the problem, or if there's anything else I can assist you with.