Thanks for the responses. Since I hate messing with smelly differential fluid, on a whim I bought one of those 12 volt boat oil changers. I never thought it would suck out the thick diffy fluid, but it did. It took about 30 minutes. Small tube in hole, big tube in drain pan. Very clean operation. I thought about reversing the tubes to fill it up, but used the hand pump instead. It took 1.8 qts just like it was supposed to, so I know it sucked it all out.
I bought the sythetic Mobil One for the first time. Someone here posted about not needing the posi additive if you use it. The limited slip additive is getting hard to come by, and $8.00 a tube. So the price worked out the same.