The GR Supra uses a popular ZF 8 speed automatic transmission that is common on most late model BMW's (aside from manual and MDCT cars). This transmission uses BMW's "lifetime oil" and thus the service tables do not mention transmission servicing. This helps to keep BMW/Toyota's "average maintenance cost" low, but it also means that when customers do experience an issue with their transmission it likely needs a costly rebuild or replacement.
To address this issue, we recommend servicing your ZF 8 speed to keep it running reliably, especially for those that see track use. The servicing includes replacing the transmission pan which replaces the gasket and filter as well. We've seen the pan gaskets fail as early as 60000km due to temperature differences and aging, causing leakage of the ATF. By replacing and renewing this pan/gasket one can prevent further leakage and it also gives us a chance to inspect the drained fluid and underside of the transmission for other issues.
We recommend doing this service every 3-4 years depending on mileage and track use