How do you check the transmission fluid on a 2001 Pontiac sunfire SE 4 door automatic with no dipstick is it supposed to have one?

I heard that GM started using "closed" transmission systems, which means there is no way to just check it. Apparently some manufacturer had multiple recalls due to the transmission dipstick becoming pressurized which would cause the dipstick to shoot out of the hole, along with the Transmission Fluid. The former mechanic who told me this said that unless there is a leak there is really no need to add fluid, and if there is a puddle of transmission fluid where you typically park, then you'll need to check the seals on the pan underneath. Removing this pan will drain the system, but one should be extreemly careful when applying the new gasket. Also, its sounds very messy. His advice was let a professional handle it if there was a problem, it would be well worth the money. I drive a 4 door automatic 2.2L 2001 Sunfire, I have over 120,000 miles, and I have never done anything with the transmission. I missed the fluid change aroung 50,000 miles because I didn't have the money, and was later informed that if you go over 80,000 miles, you might as well leave it. However, lately I've noticed a slight difference when changing gears, so I've been tempted to have it checked out.