Suit Nissan Patrol TD42 Tacho Sensors with 2 mounting Bolts.
Some models have a Single bolted tacho sensor which uses an Oring instead of a gasket.
This is the Gasket Between the Tacho sensor and the Timing Cover
Normally the Gasket will only get damaged if the Sensor is removed, But occasionally it will just start leaking.
If the sensor is removed for any reason, it is recommended that the gasket is changed as a preventative measure.