I was told from several dealers and Jeep mechanice that friction additive is only for the QD II axles with the ELSD's. There is absolutely no reason to put friction modifier in an open differential. It would serve no point and be a waste of money. I have never added friction modifier to my axles and I just hit 70,000 miles with no isses and I bought the XK brand new in 07.
As well, if anything, NOT using the friction modifier will let the fluid protect the gears better.
The friction modifier reduces the slipperiness of the fluid, to let the clutch surfaces engage properly. Same stuff they mix into ATF for the same reasons. No, it doesn't reduce slipperiness enough to compromise protecting the gears, just enough for the best compromise between lubricating the metal to metal contact and letting the friction surfaces do their job.
BUT, if you don't have any Friction Surfaces, then why compromise, use the slipperiest fluid possible.
Thanks for confirming what I suspected.
BTW, for those that have the LSD/ELSD, keep in mind, if you don't use the friction modifier, the clutches in the differential won't engage like they should and it can cause poor differential performance or the clutches wearing out quicker.
Since you guys mentioned it, I did the Transfer Case also, AMSOIL Synthetic ATF. Although I have my concerns with AMSOIL claiming their Synthetic is multi-vehicle and meets/exceeds all specs for all ATF's; I've got no problem using it in the NV-140 that calls for ATF+4. Chrysler now uses ATF+4 for all ATF uses, and in the past it was just plain Dexron or any ATF as long as it was ATF, for xfr cases that use ATF. There are no friction surfaces in the NV-140, so I'm confident the AMSOIL synthetic ATF will work great and likely better than ATF+4 in that xfr case.