My dealership tried to tell me the same thing then I sent them this
https://techlink.mynetworkcontent.com/?p=11127
at the end of it it states this
”Mobil 1 Synthetic LV ATF HP transmission fluid is required for all 8-speed transmission repairs regardless of the repair being completed.”
The new fluid is a requirement not an option for ALL 8 speeds.
I told it to the service writer just like that ( and I was polite) . Bringing g it sat to get the new fluid.