hi im wanting to change my rear diff oil before trackday season starts.
vortx is bec with sierra rear diff with lsd
any recommendations on oil?
thanks

Original fill was EP80 GL-5 Hypoid these days you are more likely to find a multi-grade such as EP75/90 Hypoid GL4-GL5 fully synthetic or EP80w/90 Hypoid Gl-5 part synthetic.

Carlube and Comma do suitable oils

I use castrol B373 in mine.

so it doesnt need a speical limited slip oil ie ls90?

No it is based on viscous coupling not a mechanical friction LSD the viscous fluid and diff gear oil never mix.

thanks