I'm guessing you have a 325? well my advice would be to find a rear end out of a 325ix (4 wheel drive version) it's slightly larger and the Diff itself is more robust! 4.10 gear too.. I found one used for $700 cnd. and it's worked great for me. bolts right up on 318/325
I have a few e30 parts for sale, updated often, discounts for local pickup/delivery. Check out my eBay
account for details.