This injector sealing ring sits between the injector body and the cylinder head, compressing to form a gas-tight seal that prevents combustion gases from escaping past the injector. It is a single-use component; the ring deforms plastically during installation and must be replaced each time the injector is removed. A failed seal produces a telltale soot trace around the injector bore and can lead to a gradual loss of compression in that cylinder. The ring is manufactured to the same cross-section and hardness as the original assembly, so it seats fully in the counterbore without requiring shims or additional sealant. On reinstall, clean the injector bore thoroughly and torque the clamp to specification.