I have always been wary of adding any “Miracle” fluids to any part of any car that I have owned. If it supposed to address a problem, it’s best to fix the problem. Having said that, I have had very good luck using Red Line gearbox oil in my Tractions. It does make it shift a bit easier and quieter. I have used it in my 1960 Saab 93F where the freewheeling would not work properly. Changing the gearbox oil from conventional 90w to Red Line made it work perfectly. It’s good stuff!
https://www.redlineoil.com/