Gears & Axles - jDo I need addiitive?

I have a Wavetrac diff in a MW chassis 9" I'm going to be changing over to Royal Purple, how much do I need and do I need the additive for this diff?

Additive is not needed and I'd pick up four quarts of gear lube. It will probably take just a little over three quarts. Bob

Thanks for the reply,