Beware of the old "tighten" routine. I had my Z at the dealer three times for a leaky diff. First two trips: 1)bolts were loose and 2)Loctite not used. R/R differential housing and replace. Now on the third trip I finally got a straight answer, the seals were bad. Unfortunately they are a special order part which arrived yesterday and will be installed on Monday-my fourth trip. My advice....if it leaks again demand new seals!
Just my .02
Just my .02