Because I'm an expert
No seriously I have spent the last 3 months sorting out an LSD and now well versed across the diffs, including every right and wrong part (I have been sent wrong pinions etc.)
Also your car is the exact same year and month build as mine.
If your on RealOEM you see 2 different diffs don't you? One is for auto and one is for manual. You can tell by the final drive being 3.08. Manual also has the flex-joint diff flange, auto has the splined on driveshaft. It is 33107609536 you need.