I went to the dealer to get the gasket/fluid for my diff (usual 10 bolt diff), and the POSI stuff.

He said that he was told awhile ago (He looked 50) to always add it. However he said recently (Whatever recently is to him) he's heard you only have to add it once, and never again (Until you change the "plates" he said).

I know it's had POSI additive in it before - do I need to add it again?

 

wouldnt hurt to add it again, i thought with any full out drain / fill up its a great idea to add that additive.

 

I think he is misinformed.

Anybody that has to be told whether to add the fluid probably isn't a "mechanic"; that may be why he's at the parts counter, and not out in the service bay. The 2 skill sets, while they overlap somewhat, don't necessarily mean that a parts guy knows everything about how the parts work.

Add it.