E30 Zone

Right I'm new to all this rwd stuff, I wanna change my diff oil on my e30. I work in a garage and we use total 85w140 diff oil, is that good enough to put in my diff? I don't know if it's a 318i diff or 325i diff.

Also how do you tell what ep it is?

Oil selection is in one of the forum stickies, but briefly, the only thing that makes a difference is whether you have an open diff or an LSD.
Open diffs want 75W90; LSDs want 75W140 WITH A FRICTION MODIFIER ADDITIVE. Use ordinary diff oil and it won't work.