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If you have the 9.25 with LSD then you've got those damn clutch retainer packs that have been known to fall off and get ground up in your teeth. They want you to check it so often for a few reasons,
reason
#1 they charge 120 per axle
#2 its cheaper for you to pay for that maint vs them filing a warranty claim
#3 it gets you back in so they can lie about what else is wrong and give the lot lizzards a chance to sell you a veh

Ok so if you want the skinny on it, if you go through deep water crossings there's a chance that the breathers could have let water in, more likely in the rear as the front goes well up into your engine bay.
Problems with having water in your diffs- will cause corrosion and damage your teeth.
When you drain it and if water has come in then itll be milky.

I run amsoil severe gear 75 140 in the rear and 75 90 in the front, the oil is rated for 100k miles and I dont plan on changing it untill then.


Oh and you can by a see through rear diff cover so you can see if waters gotten in it.