its:
Bus 8.1975 and later
When replacing the ATF fluid, you will need to loosen the sump, clean everything thoroughly and replace it with a new U-shaped rubber gasket.
Never reuse your old seal, not even using a liquid seal, leakage is inevitable.
If you have purchased a set of gaskets, this gasket is included but it is still advisable to always have a gasket in stock for the next maintenance.