So I've been thinking of how long the limited-slip rear differential is going to last in my 2004 Subaru Impreza WRX. I've been doing some reading that the viscous fluid (due to loss of fluid properties from overheating) in many LSDs might have a useful life of about 60,000 miles before effectively reverting to open-diff operation. I don't really abuse the car, race it, or do anything that would cause premature wear (I think). I would think that my type of driving might mean it would last longer. My main worry isn't about street driving, but the occasional times (Sierra Nevada in the winter) where I'm on snow/ice. It's approaching 60K miles, and I'm wondering when I would know it needs to be replaced. I looked up a Subaru parts retailer, and rear differential cases with LSD go for about $700 while rear differential cases with open diffs are under $200. I'm not sure what the labor would go for though.