Mercedes W221 S-Class 4MATIC Transfer Case Oil Leak
The 4MATIC all-wheel drive transfer case on W221 develops output shaft seal leaks at high mileage. Oil loss causes vibration at speed and eventually transfer case failure. The leak produces an oily residue on the underside of the car near the transmission. Transfer case fluid service every 40,000 miles is preventive.
Repair / Solution
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