Do i need to use friction modifier?

[TBM_F350]

I was just at the local Ford dealership getting some misc parts for the truck. I asked them about the friction modifier for the rear axle and also if they could tell if i had a limited slip in my rear axle. The previous owner had the truck undercoated and i cant see $hit on the axle tags. So i cant make out what the tags say, so i wont know until i pop the cover off. The guy behind the counter said that i should use it even if i dont have a limited slip in the differential?????

I ended up buying a bottle of it, it was only like $4.50. Do in need to use it if i do NOT have a limited slip? I was under the assumption that i only need to use it if i did have the limited slip.

Thanks,
Tim

[mech2161]

Not needed, only for LS.