hard shifting 833

I was talking to a buddy of mine the other day (he has forgotten more about 4 speeds than most will ever learn) and he told me something I hadn't heard before. He said that if it has an aluminum case it should use some form of ATF for fluid. If it has a steel case it uses 80-90 gear oil (or whatever gear oil you want to use) I have also heard others say that using synthetic with a four speed isn't a good idea because the fluid provides better lubricity (ie is more slippery than regular 80-90 and causes problems for the engagement dogs because they do not slow down like they should (or something to that effect). He said that this was true from late 70's on. So if your running an A833 aluminum OD unit from a late 70's thru 80's mopar, you need to use ATF as your fluid. I am certain he is correct but to completely remove doubt, crawl under (if you don't already have the info written down somewhere) and get the model number off of the trans housing and call your local stealership and ask someone in service or parts what the recommended fluid is, they should be able to look it up.