So I picked my car up from service after having several things fixed and diff and transfer case fluids changed. Everything seemed fine until today. I started feeling like I could feel and hear a binding in the rear. I got out, checked the truck out and didn't see anything wrong. I could see where they had filled the diff because it was stained with fluid residue, and thought I was just being paranoid. Took her off road and felt the binding again. Put on 4x4i screen and noticed whenever the rear diff locked I would feel the binding. I pulled out my paperwork and with horror realized they had used the same fluid for the front and rear diff, aka. NON-Locking diff fluid in my locker equipped LR4. I called the dealer, they said to drive it back in and they'd check it tomorrow. I'm petrified they have ruined the rear locker. They said they are going to drain the fluid, put the correct fluid in and drain that, and refill. For all I know it's already sustained irreparable damage and is toast. What should I do?