Serg has built 3 diffs for me.
3.15 40% lock
3.46 60% lock
3.91 40% lock
That is my car in his ad. He rebuilds the diffs and they hold up. I autocross my car and put more stress on the E36 diff than anyone else in the country and have not had a failure with anything Serg has built for me.
You need to be aware that the E36 diffs are held in by 3 bolts. I know you have had the rear 2 out when you had the diff cover off before. But bare in mind that the front bolt on your car is 14mm. If you get a diff that isn't setup for a BDR it will be 12mm. You will have to tap the hole in the diff to 14mm.
BMW E36 3.46 LSD POSI DIFFERENTIAL LIMITED 40% LOCK 325I M3 BACKDRAFT COBRA | eBay
Kevin.....