I don't understand the thinking behind filling a transmission when new and driving it 200,000 or more miles on the same fluid. Here are some ideas if you decide to change it.

Transmission fluid change? Do this one yourself. It’s very easy. Go buy about four feet of ½ inch inside-diameter clear plastic hose and a hose clamp the right size for it. This will go over the fitting on the radiator. Also, buy a funnel for filling automatic transmissions, and a case of ATF.

This method has worked for me. I'm sure there are other ways of doing it too. With the engine off, loosen and remove the top fitting on the passenger side of the radiator. Use a wrench to keep the fitting from turning in the radiator. Use a rag to catch any fluid that might come out. It won’t be much. Put the clear plastic hose on the fitting and snug it down with the clamp. Run the hose over the fender into a container with measured marks on it. Start the car and run it in park until two quarts are in the container. (The fluid comes out at a comfortable rate. No rushing around.) Shut off the engine and pour two new quarts into the tranny through the dipstick. You’ll need the special funnel for this. Run the engine again and pump out two more quarts, add two more, etc., until the fluid runs out clean. I think it takes about 10 quarts for the job, if I remember correctly, maybe even 11 or 12. When you’re convinced the fluid is coming out really clean, remove the clear plastic hose and put the original fitting back on the radiator and snug it down, holding the male piece so it won’t spin in the radiator. There is no o-ring. Run the car and check the connection for leaks. Remember, if in doubt, add a little less fluid rather than too much. It’s a lot easier to add a little bit later than to drain fluid from an overfilled transmission. Check the fluid level before you start the job. If it’s right, and you cycle the exact same amount, you should be OK. From my experience, though, it’s better to add a half quart less, then check with the dipstick, and top it off to get it just right.

You’ll find the job is easy and clean if you are careful. You’ll be satisfied that the job was done correctly.
--
Thanks for all the help. DougC 1981 242, Turbo bars and wheels, M46............1993 245, B230 NA L-Block, M46, Turbo bars.