DOn, everyone is kind of right. 40 years ago 20 wt engine oil was about as good as you could get. These days they make special oi for hydraulics and transmissions since they dont get too hot and cant boil off the condensation (water) like a motor can. These are trans-hydraulic fluids. You can get at farm store or WalMart. It is a 20 wt oil, but not motor oil. Steering fluid is about the same story. It has special additives to improve it over engine oil for special uses. Personally i would go with the trans-hydraulic fluid in the hydraulic and steering systems. To help confuse you , some people use transmission fluid (DEXTRON). Again, this is basically the same viscosity, but special additives which you probably dont really need.