04 Titans have this problem, its almost always a indication of impending differential failure....RARELY its just a bad seal on 04 - early 05 titans. Dealer will probably say its a vent issue.BULL SH$%!!! As a auto tech of 15 years and titan owner I've seen more bad rear titan differentials then I care to. NISSAN NEEDS A RECALL.
Leakage happens when bearings start to fail and allow gear set and thus axles move around more the allowable . In turn putting excessive loading and heat on components. Common to see spider gears with enough clearance between teeth to throw a wrench through it. If it leaks oil at rear axle, axle shafts must be R&R'd. To do so differential needs to be opened up..
AND SHOULD BE INSPECTED FOR PREMATURE WEAR. Nissan doesn't rebuild differentials for liability reasons. New differential is a UPDATED UNIT (if that doesn't screem nissan is aware of this problem, when the play blind and deaf to it) Also. upadated gear lube spec 75W-140 SYNTHETIC LUBE ONLY! MOST fail around 50-60k miles. Also front differentials fail around same mileage and same wear. In my. professional opinion its due to insufficient grade gear lube installed at factory and if serviced at dealer following Nissan's spec lube at service intervals. CAUSING. EXCESSIVE HEAT AND PREMATURE WEAR. Hence the new updated differential with. "heat dissipating" aluminum cover and 75-140 synthetic lube. Its a $2800 repair. depending on your local dealerships labor rate. Front differential $1300