Buying off eBay is always a bit of a gamble, but sometimes you Win! I ordered a $99 3.91 Open differential(M96) out of a Lexus. The intention was to try out the lower ratio and if I liked it I would swap the ring and pinion into one of my BRZ diffs. Well the diff came in today and much to my surprise it turned out to be a 3.91 Torsen LSD!(M98)
Looks like I paid for a M96 and got a M98