Is this Supertech 80W-90 gear lubricant safe for the 3 speed manual in a '55? I used this in the rear end, and have a lot left over. The back of it says "Protects against rust, foam, high temperature and corrosion of copper or bronze bushings."

 

I used it in my 3-sp for quite a few years. I had the trans apart afterwards, and there was no damage to the bronze parts. Most of my usage during that time was around town. After hearing from several sources that StaLube 140 GL-4 was a better choice, I switched to that. Very small improvement in shifting, and I've used it on long highway trips, without any concerns about the bronze.

Any damage that GL-5 could do, only occurs at high oil temps (continuous highway use in summer).