8 speed transmissions
 

I just called the dealership to ask when my transmission needs a fluid swap, they said the transmission is a sealed unit and doesn't need maintenance.

Is this true?

What Year, Make & Model? What does the "Owners Manual / CD call out in the Maintenance Schedule.
All transmissions should be serviced at some point in their life cycle. Chrysler/Fiat/Stellantis has been using a "Sealed Transmission" for many years. (Wife's 08 Sebring, no dipstick)
The aftermarket makes and sells a "Universal" dipstick tool that is used to properly check and refill the trans. Stay away from "Fluid Exchange/Flush" systems. Drop the pan, replace the filter, clean the muck out and properly refill with correct fluid. (Most likely ATF+4 but check and be sure)
Find a new dealer........

2015 Chrysler 300S

So I called around and found a transmission shop with experience on these transmissions. They said its best to do a fluid and filter swap at 50k-70k miles on them.

I'll be having it done on the 27th.

I don't know why dealerships aren't providing this service and why they are telling people this is a "lifetime fill" of fluid.

To my mind and limited knowledge, there is no lubricant that can do that.

Are dealerships telling people this so they'll burn out their trannies at by 100k and buy new cars?

I don't know.

What I do know is that I want to keep the car a little longer than that, so I'm glad I asked around about this.