Rear diff oil additive friction modifier

[ARiley23]

Changing my rear diff. Fluid and looked in manual and it says when changing add an additive friction modifier.
My question is is this important to add like without adding it will burn up my rear?
Thanks!

98 Eddie Bauer 5.4

 

[Bedrck47]

I would think if it WASN'T IMPORTANT that Ford would not have put that information in the owners manual

 

[JUST4FUN]

Yes the modifier is for limited slip rear end ,but not necessary for an open diff so find out which you have

 

[tonydiv]

You'll feel a notchy-ness in the rear if you don't add the modifier to your ls diff.

 

[98EXPnSRQ]

Use Royal Purple, it already has the modifier in it.