I too tried to buy 80/90 "Castrol Hypoy C" gear oil. Turns out no Castrol gear oil available around here unless I buy 35 lb buckets (about 5 gallons).
So I used Valvoline.
The Valvoline tech line sent an email to me "the Valvoline High Performance 80w90 Gear Oil contains 3% limited slip additive in the blending of the product.
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