How to identify differential?

[roky]

since my 240D differential has died an early(120K) death, i am beginning to wonder if this whole rear end was replaced at some point, and is not original -- i know that someone had done a very sloppy job of removing/reinstalling the diff cover at one point -- the numbers stamped on the diff case are :028941, followed by the ratio, 3.69 -- it would be helpful to be able to identify a differential by number, as i also have a replacement arriving by ups, would like to be sure its compatible before i put it in this weekend

as always, thanks for any help offered

roky