Symptom: Appreciable loss of oil from somewhere above the sump parting line, at the back of the motor.

Likely cause: Oil pressure sensor's plastic body has shrunk, allowing oil past the base's swaged lip holding it together.

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Note 1: Thread is M161.5mm, you can use a sump plug in an emergency or remove the sensor and braze the orifice shut. Use a new dead soft metal washer or copper crush seal (16mm ID) where possible.

Note 2: OEM specification as observed - maker FAE, trip pressure 0.5 Bar, part number 12460, suffix 39L

Note 3: Many other pressure sensors will fit, you may wish to use another of the same thread but be prepared to replace the connector (single wire type).

Repair method:
Loosen RH front wheel, jack up car, place front on stands and remove RH front wheel. Remove splash shield covering crank pulley, and set brake pad wear wires to one side. Unscrew 11mm headed M6 bolt holding cable bracket to timing chest beside sensor. Clip or cable tie out the way. Start motor and confirm leak is from sensor, now visible.

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Use 22mm deep wall socket to remove sensor. Repair or replace as planned, refit and test before connecting up harness or reassembling covers/wheel.

Mystery PRV Oil Leak (XM, 605)-dry_repair.jpg

When confirmed leak repaired, degrease back of block, subframe and other oil-tainted areas. Reassemble inner splash shield, refit pad wear sensor wires, reattach wheel, lower car and torque wheel bolts.

Completion: Drive car, and remember to savour the smell of nil depreciation in the mornings.