Originally Posted by Z K
You only need the FM (aka Friction Modifier) booster if your diff is making grinding noises. All it does is make the noises go away. Otherwise you can use the regular LSD diff fluid which is a lot less expensive.
mine never made noise but still opted out for the friction modifier which is a lot compare to the regular..
ALSO FYI if you guys are interested on 15 bucks a bottle contact MERC... they have it without the Friction Modifier for less than half a bottle compare to BMW...
Here you go...