My F-150 is doing fine, but I was hoping you guys could help me with the limited slip rear end on my wifes '02 Mercury Mountaineer. We bought it used, and I noticed we could spin just one rear wheel going up our steep, snow covered driveway. I drained the fluid and replaced it with synthetic with the friction modifier, and no difference. The tag on the diff and the code on the door confirm it is LS. Not knowing much about this end of the car, I'm stumped. Are the clutches shot? If so, what am I talking in $ to replace them?