Originally Posted by 99MazdaB4000
The diff is fine, just leave it.
If it ain't broke don't fix it, part of Fords gimmick to bring you in to pay for parts and labor.
Preventative Maintenance actually does work, If we used that logic we would never change the oil til the motor locks on us. Sure you would need a new motor about every 25,000 miles but hey you would have a new motor which is a hell of alot better than 40 bucks every 3000 miles...
Diff fluid does need to be changed, every so many miles cause oil does loose its lubricating ability over time, also clean fluid wont have any debris it it that can damage ring and pinions or L/S