Ruben, Volgapower has a Torsen diff and they don't apply to the "if both flanges spin in the same direction" test. Torsen diffs act differently as they require torque to lock. All Z3's came with either Torsen diffs or LSD's. I believe the M roadsters and M coupes came with LSD's while all other non-M Z3's came with Torsen diffs. Torsen diffs are commonly marked with an "R" either on the case or on the identification tag. LSD's are commonly marked with an "S". Here's pics of all three for comparison:
