Type of Fluids For Old Caterpillar

I am changing the fluids in the rear end, front end, and planetary's. The manual states to use 30w. I took out fill plugs and it smells like 30w not that strong gear oil smell. Should I follow the manual and use 30w? Basically everything in this machine calls for 30w or 10w depending on temperature in manual. Or is a gear oil like 80-90 better in this old Cat? 1963 966A. Thanks.

Type of Fluids For Old Caterpillar