If you notice the description of Chevron Meropa, it is listed as an industrial gear lubricant and as such was not blended with automotive use in mind.
Lubriplate SPO gear lube is still available in SAE 250 and it is a straight mineral.
https://www.lubriplate.com/Products/...O-299/SPO-299/
The presence of sulfuric and phosphoric acid is always marked by the smell. If it is in low quantities such as GL3/4 then it would be considered mild EP and not extreme. Since it is industrial grade, it doesn't have to be rated for automotive use. The industrial EP ratings can be misleading when comparing them to the normal API automotive grading system. Any tarnish of copper is a sign of extreme EP and heat & moisture just make it worse. The stuff might work fine with no detrimental effects but it's good to know the risks. Modern industrial uses likely have no yellow metals to worry about. Most have huge ball or roller bearings. Phosphor bronze has copper but it also has tin and phosphorus so the copper test only tells part of the story.
https://www.nyelubricants.com/lubric...pper-corrosion
Older helicopters had hydraulic dampers but none do now days. I still work on the old Bell 47 helicopters and they used to have the who-die dampers for the stabilizer bar but they only used Mill-H-5606 hydraulic oil in those. They had so many problems with the stabilizer bars that most folks operating them install a N0 Bar kit and did away with them. It certainly cut down on maintenance times but it made the flight controls a lot more sensitive.