The transmission fluid on a 96 Pontiac Grand Am SE is put into the filler tube on the left side of the engine. It runs directly into the top of the transmission and also contains a dipstick to check fluid levels.
There is no dipstick to check the transmission fluid on a 1998 Cadillac Catera. It can be checked by opening the fill plug on the side of the transmission. If you are at that point you might as well change the fluid if you have over 70000 miles.