Rumor has it that it is a damper balanced for for stock gears. Once you change gears you acn remove it without any issues. I have done this on 3 cars including the Bullitt after gear changes, no trouble.
Mine came off, even before I put the aluminum driveshaft in. There was a hint of additional vibration with the stock driveshaft, but none now with the aluminum driveshaft. A bunch of unsprung weight that doesn't need to be there.
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