i have a torsen limited slip in my truck and am going to change the rear axle fluid. do I need to use a friction modifier, or not? I know the torsen is NOT a clutch driven unit, as are the stock ford trac-lok axles. I have the 75W-140 rear end fluid from motorcraft, as well as friction modifier, just not sure if I should use it. the parts counter guys told me they weren't sure if it needs it or not, but that it wouldn't hurt to put it in there.

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2002 Ranger FX4
4.0L SOHC, 5R55E Auto, 4.10 8.8 Torsen, 31x10.5/15 BFG ATs