The sealed transmission concept is a load of crap. Basically a scam to try and force the owner to take the car to the dealer for all tranny checks/service. I've owned two vehicles that claimed to have sealed transmissions. Do enough research and you'll figure out where they hide the dipstick or cap to access the fluid since your owners manual won't tell you.
If you can find it, be sure to check it with the engine warm and running. Tranny fluid in good condition will typically have a reddish tint and kind of a sweet smell. Fluid that needs to be replaced will be much darker, brownish black, and will have more of a burnt smell.
For future reference, I would recommend a drain/fill instead of a mechanical/power flush if your car is over 100K. A lot of high mileage cars can have issues with a power flush as the process often stirs up debris within the transmission. Buy a case of fluid. Gravity drain as much as you can, measure and fill with an equivalent amount of new. Drive around and repeat until you've added the case of new fluid. Obviously, you'll be draining partially new fluid each time, but as it mixes the fluid should become more red and you'll have 70-80% new fluid in your tranny when finished without the risks of a power flush.