When I went to my dealership to get my windows fixed, they recommended changing the rear differential fluid, but wanted $149. This was already on my to-do list, but how hard is it to change the fluid yourself? I thought all you had to do is unbolt the fill plug on top so it drains faster, and unbolt the drain bolt. then re-fill, kinda like changing oil... does it seem too easy, or is that all there is to it? also, where do I get the synthetic fluid, what brand, how much, etc...

thanks in advance, John