If you get down to the actual spec of the John Deere Corn Head grease it is the correct stuff. What you need is a self leveling grease. I'm not saying that other stuff won't do the job. I will say that 90 gear lube is way to thin and in a fresh rebuild I'm sure it will stay in the box. What I would question is that under the stress of working the steering box that it will hold up.

Don