Helicopter inspector reported the flight crew had a tail rotor gearbox chip light illuminate in flight. Inspector found incorrect records and procedures for the gearbox that resulted in non-compliance in maintenance tasks and logbook entries.

Narrative

A crew out on a electronic news gathering (eng) flight experienced an in flight illumination of the tail rotor gearbox chip indicator light. A precautionary landing was made at ZZZ. A mechanic was dispatched with the manufacturer's instructions and sufficient oil to flush the gearbox and do the required post check runs. No further problems developed and the aircraft was placed back in service. As I went to the aircraft's historical record cards to check on the gearbox total time and history; I was informed that the serial number did not match the currently installed gearbox; an overhauled gearbox was installed on Date and the one in the aircraft records had been removed.The work order with the gearbox change was sitting on the office administrators desk and had not been reviewed by the Director of Maintenance and myself the Chief Inspector. Each time a gearbox is changed; the manufacturer specifies certain post installation inspections be performed at 2-8 hours; 10; 20 and 30 hours including an oil change after 2 hours and recurring chip plug inspections. These were not done and the aircraft had been returned to service with no follow on maintenance recorded in the aircraft records. This shop has repeatedly just installed components without concern for the required post installation checks. The manufacturer's manuals were not consulted during the gearbox change.[Contributing factors are] Pressure from operations to get the aircraft back in service for the customer closing out work orders on the weekend when no office personnel are on duty. The lack of employees in the records department to review and monitor the work orders for proper completion and ensure procedures are followed.