2007 Pontiac Wave - transmission service

I have a 2007 Pontiac Wave which has about 84,000km on it (52,200mi). It is my understanding that it's basically the same as a Chevrolet Aveo. Now, here's my story:
I got an oil change done at the dealer about 6,000km ago. I was told at that point that my vehicle should get a transmission service done. Last week, I got an oil change done at another place and they checked my transmission fluid (it was brown). They recommended I have that changed. So, I book an appointment with a different local shop to get the transmission serviced. They told me that they cannot access it because it is a "closed transmission" and I should refer to my dealer. So, I finally book an appointment with the dealer.
I drive in, and they say, "Oh, your vehicle does not need a transmission service done". I asked if she was sure and she went to get the head technician, who confirmed it. Now I'm confused. When I first got my oil change at the dealer they tell me I should get my transmission serviced soon (and that the warranty depends on it), but when I actually go to get it done they say it's all internal so it's not required. Can anyone else confirm this with me and explain to me why this is the case? The dealership never explained why; just told me it didn't need to be done.
Upon looking through my owner's manual, it states nothing about a transmission service and nothing about checking the colour of the transmission fluid. It just says to check the dipstick and make sure there's either enough fluid or not too much fluid. Any help regarding this matter would be appreciated :)