I'm guilty of changing stuff too soon, or at least sooner than the OEM "recommended" intervals. I've been changing diff, tranny and xfer case fluids at 30,000 miles. Each of my vehicles have in the neighborhood of 250,000 miles on them. Not a single mechanical failure (lubricant related) among them and everything operates as close to a 'new' vehicle as you can get. I've upped oil changes from 4000 to 5000 miles recently and I rotate the tires at the same time I change the oil. Yes it's sooner than you could get away with, but I doubt the OEM's want our vehicles to last forever. If it lasts forever, you'd be less inclined to buy a new one.
