Adding a friction modifier to an LSD

[Sour Kraut]

Have picked up an LSD for my E36. Is there any kind of consensus regarding using a friction modifier before it actually starts making a noise?

I'll be using Castrol SAF-XJ gear oil in the diff; should I wait until it starts complaining before adding the FM or use it from the outset? (I don't know how many miles the diff has already done)

[E30M3SE]

SAF-XJ should be fine on it's own, so long as the diff does not have any other issues.