Hello and welcome to 2CarPros. There are hundreds of opinions on this. For me the issue is simple. Run the engine some. Then pull the transmission dipstick. Now look at the fluid close, let some drip onto a clean piece of white paper to make it easier. If the fluid is clean and not burnt and you don't see a lot of black or metal in it, change the fluid and filter out.
If it is dark brown or black and smells like it's burnt it becomes a toss up. That fluid suggests that internal parts are already worn and have gotten hot. At that point the transmission is on life support. On those I would still change the fluid, however I would also tell the customer that there is a good possibility that the transmission could fail soon because of the original neglect.
So let the fluid tell you what it needs. The other thing is that the transmission could be close to failure anyway and changing the fluid does nothing to help or hurt it.
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Sunday, May 5th, 2019 AT 4:20 PM