should the GM friction modifer stuff be added to a Locking Diff?

im askign cause i am changing the fluid on my 2002 S-10 and it has a locker (i think an Eaton locker, not sure) and the Tech at the chevy dealer told me to use the additive, but the owners manual and another website said to NOT use the additive on a locking rear end..

 

im confused.

if it has clutches, use it.

if its just a mechanical locker, with no clutches, then its not needed.