The system has never been tested as a whole:
The emergency lubrication system was certificated by the EuropeanAviationSafetyAgency(EASA). Certification included a test on a ground rig in which the oil was drained from a MGB and bleed air and Hydrosafe 620 were sprayed into the gearbox. The test demonstrated that there was no significant damage to the MGB after over 30 minutes of operation. Although the emergency lubrication sub-systems were tested individually, no test was carried out on the complete system, either on a test rig or installed on the helicopter type.
from the G-REDW AAIB report