As a fix for what problem? If it’s a noisy box I’m not sure it would be any more effective than sticking a banana in the gearbox. I would be a bit suspicious of it curing a leaky shaft seal but it might work on a leaky paper gasket joint. But the thing is it claims to make the oil sticky – which is not very selective, so you have to wonder how the bearings would like it. It’s expensive too. But it’s only listed for the 1898cc engine which I doubt is fitted to your car.
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!
I must confess to being wary of additives too. That is why I asked.
I don’t have any significant oil leaks, maybe an odd drop. Its just a bit noisy but I think that is not uncommon for traction boxes. I don’t know if mine is noisier than others or not. Bearings and seals were checked/replaced during the car rebuild.
I came across a “sticky” oil some years ago. It was recommended for industrial gearboxes. It was not thrown off the gears when they were spinning, maintaining oil on the teeth. I don’t know if it would have affected synchro-meshes.
A gearbox rebuild would be nice but it ain’t broken so I won’t fix it yet.