I have a 2008 Chevy Cobalt with 75000 miles, I've never changed the transmission fluid before, and i don't know if previous owners have either. Would changing 14 year old fluid mess up my transmission, or just if it was fluid that has been used with a lot of miles.
If you want to go ahead and try it might not be a bad idea, but like Scotty has said many times....
save the old fluid that way if it does start to slip you can put the old fluid back in.
Just drop the pan and change the filter and fluid. Don't do a complete flush. It should be fine I've seen people wait till 100,000 miles and be fine but if you are gonna do it I will do it sooner rather than later.
Changing the ATF cannot mess up your transmission, unless it's messed up already. And I don't see why it would be with only 75k on it.
If its 14 year old fluid and has little or no color, I would probably just try to pump out say 2 quarts and fill back with 2 fresh quarts to get "some" wear additives back into the system. Disturbing the entire system after that long could be a crap shoot. If the fluid looks more pinkish, a change may be OKAY.
I drained/refilled the ATF pan on my 02 Mustang at 68,000 miles. This was the first time this has ever been done on this car. I haven't had any changes in tranny performance from doing so.
A colleague of mine had the same and he did the same (Change transmission fluid) to keep his car for longer. Unfortunately, it did more harm than good and within 2000 KM the transmission blew out.
Like Uncl Scotty says, if you haven't done a oil change in American cars for over 60 k kms, do not touch them.
Drive it as it is.
Scotty did not say "over 60k kms"