Transmission gasket?

Does anyone know where to find an actual gasket for the transmission of a 24 Mazda 3 turbo? The dealer told me they don’t have any since they use rtv gasket when I asked if they change the gasket and filter when doing a transmission fluid change. They don’t even change the filter they just use a fluid exchange machine and don’t even drop the pan, then they justify 500 bucks for it.