Originally posted by jimbo
Hi Joe-

According to Royal Purple the additive is built into their synthetic gear oil. I assume this is true?
There are only two true synthetics: Mobil-1 and Amsoil. They say the same thing as well about the LSD additive, but it's more applicable to viscous type LSD units which the VX doesn't have. Some people experience chatter from the diff without additional additive, so you could take a chance or just spend the extra $5 and put it in while you're doing the service.