Why did the guy sell it? Its hard to get an honest assessment from dealer to trans shop because no one wants to touch them. For it to fail at 40k its either been beat to crap its whole life or its not in as bad as shape as your being told.

I dont know if app you can buy for your smart phone (https://alfaobd.com/) goes as deep into the trans as needed. I have known some told as you only to replace a pcm or noid pack.

You might consider a second opinion just to be sure.

Are you on this site... https://www.dodge-dart.org/

If you are not, the head mod Alpinegreeneon has more fiat info and charts and diagrams than any ive ever seen..... almost seems like he connected to fiat hes got so much.

You might check with that site and person as the darts have lots of issues and hes got all the info.... some may not like what they are told but the guy is sharp.

Some on there, the younger guys have not winced at pulling there trans to fix it. And many times its not been as bad as they were told.