Best gear oil?
 

I'm putting on my Mac differential cover and don't know what weight of fluid I put back in the differential. Would a synthetic like redline be a good idea? I have an auburn diff. so I think I still need the friction modifyer, but whats the best oil to refill the differential with?
Thanks,
Chris

I use valvoline semi-synthetic with great results. Be careful, some fully synthetics are not recommended for traction locks. the semi is good stuff, and all you really need.