The aircraft was enroute to Mount Buller on a medivac priority flight after having departed Essendon. During climb out to cruise level, the aircraft experienced a caution advisory indicating low oil pressure of the number two engine. The crew initiated emergency procedures and completed an uneventful precautionary landing near Thomastown. Further investigation revealed oil leakage in the area of the number two engine deck. An engine magnetic particle detector receptacle was found loose and backing out, because of a failed lockwire, thereby causing the oil leakage. The engine number two and three modules were replaced as a precaution and the aircraft returned to service.