Differential Gasket
A seal placed between the differential cover plate and the differential housing to prevent gear oil from leaking out.
A differential gasket is a precut seal made of paper, rubber, cork, or composite material that is compressed between the differential housing and the rear cover plate. Its job is to seal the high-viscosity gear oil inside the differential, protecting the ring and pinion gears and bearings from running dry.
Because differentials do not have oil filters, the gear oil accumulates fine metal wear particles over time. Changing this fluid involves removing the cover plate (on many vehicles), draining the old oil, cleaning the mating surfaces of old gasket material, and installing a new gasket with a fresh fill of gear oil.
If the gasket deteriorates or the cover bolts become loose, gear oil will leak out. A leak is often noticed as a dark oil stain on the differential cover or on the ground. If left unaddressed, the fluid level will drop, causing the gears to overheat, whine, and eventually seize, leading to expensive drivetrain repairs.