I recently took the plunge and bought a new-to-me used limited slip differential off of eBay. It came from an ’89 325is with 117k miles on it. It is nice and clean with little resistance while turning. It has 3.73 gears which are the same as what I was already running. This past week I decided I would put it in with a pair of new drive axles and brake lines. The new lines are also from eBay, I cannot remember the seller or brand but are braided steel wrapped around Teflon and look the part.
So far I am pretty happy with everything. I am hearing and feeling some grinding from the limited slip. I think a change of fluid may help that. My wine that I could hear between the differential and cv/drive axles is gone. The brake lines and pads (Hawk HP+ up front) really feel great. The pedal feels much stronger than with the old HPS and rubber lines. The only complaint I would have is the squeal as they can get quite loud.
All in all, it took my dad and I 5-7 hours to complete all the work. It really only took that long because of how rusty some of the components had gotten. My right front wheel took about an hour to get off while the brake lines took even longer.