Battery draining overnight

Here’s my alternator. I’m trying to decide if I want to follow the guide that was previously posted on this thread or just send it in. The guy at Powermaster said if I sent it in they’d look over it and repair anything on it and just charge me for the parts. I tested it with an ohmmeter and it has continuity between the stud and case. If I were to open it up I don’t know what I’d do after that point.
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