The eaton trans should not ude multigear 85/90 or multigear 85/140 but a 50 w motor oil or aershell in the white can which is airplane engine oil that is mineral oil 50w. a eaton trans has in the past had a materal on the syncronizer that is beleived to be damaged but the multigear oil. The mack trans has a disc plate clutchpac for a snycronizer and untill the snythectic oils came out you could use quote bu mack multigear grease and unless i was in hot country i would use 85/90 and not the 140. the 85/90 is too heavy in a eaton trans also if you are in trhe hot coutry and pulling hard. The oil temp will be higher on that oil than if you had a 50w engine oil in it. I know alot of guys run 85/90 multigear oil in their eaton or roadranger but liston to eaton or go to their website they will ask for snythetic but when it is not under waranty i say and have and will use a 50w motor oil and you will see a cooler oil temp. If i had a 85/90 AMI GL5 gear oil or 85/90 in it now i would not change, if you are not working it in the hot country and pulling at long hours at a time it will be maybe ok but if it was enpty i would use the 50 w in the eaton. If you do a google search you can find some good sounging oils that is supposed to go any where but the reason i think that most gear makes or trans makers ask for a snythetic by a certain part # to get the waranty is they know that there is a magic oil out there that sounds good and supposed to be able to be used every where but they want to know what is being put in there and you have to have prove in order to get waranty.