Oil Type: Gear oil API GL-4 or GL-5
Recommended oil viscosity: SAE 75W-90
Automatic Transaxle: 1ZZ-FE engine: Up to 2.9L
2ZZ-GE engine: Up to 4.0L
Automatic Transmission fluid 'Type T-IV'
Change Automatic Transmission fluid only as necessary
When changing the Automatic Transmission fluid, use only Toyota Genuine AFT Type T-IV (ATF JWS3309 or NWS6500) to aid in assuring optimum transaxle performance.
Notice: Using Automatic Transmission fluid other than Toyota Genuine AFT Type T-IV may cause deterioration in shift quality, locking up of your transmission accompanied by vibration, and ultimately damage the automatic transmission of your Celica.
What do they mean by "Change Automatic Transmission fluid only as necessary"? Does this mean it does not need to be changed based on age or KM's travelled? Only when it drops to a low level?