GL-5 was the standard going back to the seventies and replaced Mil-L-2105 that dated back to WWII. The milspec was cancelled some time ago and the military now uses GL-5.

Decades ago when I wanted to change the axle oil on my 190E 2.6 (one change recommended by MB for new cars at about 1500 miles or so.) I looked at the MB recommendation, and it was 85W-90. I searched in vain, but could only find 80W-90 GL-5, but did see a Pennzoil 85W-90 GL-5. So I contacted them and they said they did not sell their 85W-90 GL-5 gear oil in North America.

I was rather irritated that MB recommended a product for US market cars that was not sold in the USA.

So the Pennzoil 80W-90 GL-5 has been in the axle now for close to 30 years.

Duke