The only reason I used a "new" cover was so I could get the bushing pushed out ahead of time so I didnt have to 1) take the old cover off 2) clean it 3) Go to the machine shop...
The diff. cover that I used looked like my old one but I used a wire brush and castrol super clean. So, yeah, it is bare aluminium.
There isnt LSD. 1991 318iC's came stock with open 4.27.