That depends upon your abilities. It is slightly cheaper to rebuild the transmission, but unless you have experience in transmission rebuilds, I dont recommend it as you can end up with a transmission that doesnt work and more issues.
If you dont have any experience in rebuilding transmissions, then I would look for a low mileage transmission and just swap it out. While a little more than a rebuild, it is quicker to do this and just be done with it.
With the combination of symptoms and fluid color and smell, along with the metal shavings, I think you have more than just the overdrive assembly, which is why I recommend just installing another transmission altogether
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