00 grease is good. Corn head grease is not self-leveling...which is what your steering box was designed to use. I mix corn head grease about 50/50 with 90 weight oil to get a blend that is thicker than plain 90 weight but is still self-leveling. If you can't pour the grease you're using into your steering box then it is probably too thick to be a good choice. Good luck. I bought the last corn head grease (believe it or not on another forum a fellow refers to it as corn bread grease) at the John Deere store.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end