Steering clutch and final drive fluid

What's the best fluid to run in both. I have read that SAE 30 or 80w-90 gear oil will work.

Better tell us a model first.
regards
Mike

Sorry. It's for a Cat 951C.

Cat always called for the same 30wt oil that was used in the desiel engine to be used in the transmission and steering clutches A 30wt oil with series 3 ,CD rated
or TO specs current
Final drives was changed from 30wt to 80/90 wt gear oil
Personally I would use 80/90 in final drives ,as I have seen a lot of final drive failures in 941 & 951 tractors when 30 wt was used
In a warm climate ,I would even use 140 wt ,and it was used by CAT for a while in all final drives