I would recommend you get this done ASAP. I was disappointed to find a huge (garbage can lid) size puddle of rear differential fluid in my garage. Still have not gotten it up completely, and it smells real bad too.
Dealer said sometimes they just leak a little, other times they dump. Lucky me, I got the dump. Also, if the leak progresses fast enough, your rear could 'lock up' while driving, which of course is a huge safety issue.