This gearbox sealing washer sits between the transmission housing and the output shaft or cover plate. It prevents oil leakage from the gearbox by compressing into the joint face when the retaining bolts are torqued to specification. A hardened or deformed washer loses its ability to maintain a seal, leading to visible oil weepage along the mating surface. This component is manufactured to the original geometry so that it matches the housing's seal groove depth and bolt-hole alignment without requiring shimming or modification. On reinstallation, clean both mating surfaces and replace the washer rather than reusing the old one.