Thanks for all the comments.
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.
Which RedLine oil did you use Larry? MT90?
Thanks again for the input.
Roger G