My rear diff started whining after being stuck in the mud for about an hour. I got it home and swapped the fluid but found no water. The fluid was very runny and dark which I thought was odd since it was only about a month old. I swapped the fluid with 75-90 and the whine didn't go away. I just learned that the LSD requires 75-140 and I'll be doing that first thing in the morning. My question is:if does the whine indicate that it's too late and the clutches are worn? I'm a differential noob and any input would be greatly appreciated.