I used one of these on my bucket and used the Ford spec grease and didn't fill it totally full. I used the Ford spec because it has a higher viscosity rating then the rest of the 'standard' chassis/wheel bearing lubes. The seal never leaked. The original cast iron gear that I bought from Total Performance - leaked, but not too badly and it was over filled. These Corvair gear boxes are rack and sector rather then the recirculating ball that most steering boxes have so do need some room to move where the ball type just follow a closed sheet metal cage.