Gear oil for trans and rearends

[Johnboy]

Take this for what it's worth most of this is second hand info.
The gear oil issue was out of curiosity on my part the reason I asked is I personally know a few people from down in the sticks of Kentucky that run 80-90 in everything trans and rears one, it's cheaper two,it last longer three, it lubes better my personal opinion.
Now think about this eaton told me the sulfur content is to high and eats the brass or something to that effect in 80 -90.
Personally I think they came up with this b.s. because nobody would buy synthetic oil because of the price.
Food for thought one of the fellows from ky got 1.7 mill on the original rearends before he changed them due to a worn barring and he wanted a different gear.
Maybe someone on the forum can answer this what's the difference between a drive axel or a trans from the days of 80-90 and the ones today I bet some of the parts interchange.
More food for thought I can show you a freightliner that's in the shop now for the third rearend in a year and it's 2 or 3 years old.