Mine (bequeathed by my Grandad who bought it new), has had new/clean Engine oil in the hydraulic system..
10/30 would be as light as I would use in the engine or the Hydraulics.. unless the temps drop below 0 and stay there..
Synthetic oils may not get as stiff with temp change..
The Transmission gets really stiff on startup, until it runs and warms a little...makes the Hand Clutch drag ( Thick oil.)....!
One suggestion I will make.( I do this myself)..
In the Fall, I add one Qt of Rislone to the engine oil.. That will slowly and safely clean up the engine ( and thin the oil some) change it in the Spring..!!