http://bentasker.i2p/posts/documentation/vehicles/709-vauxhall-corsa-d-oil-pressure-switch-replacement.html
After some use, they eventually fail and start to leak oil inside your engine compartment - worse, some of this oil can get pushed back into the wiring, and then drawn up into the loom via capillary action - left long enough, a failure of this switch will be followed by failed lambda sensors, airflow sensors and then ultimately, the ECU.