Thought I'd throw this out there as I've found many older vechicles required oil like GL-4.
Including foreign cars, muscle cars, vespa motorcycles and on and on!
Found this paper-10 pages long after searching GL-4. Good explanation with pics, graphs, specs, etc.
Too long to just upload paper to this site!
I barely can get on the computer so I do not know how to just copy web page site address so if interested you will have to type it in your computer. Sorry!
widman.biz/uploads/Transaxle_oil.pdf
This was wriiten to a forum for Covair transaxles, But info is the same for our cars/trucks for GL-4/GL-5 questions
If someone can correct this address to easlly connected to, I'll be your debt.
Doug