It depends on what is in there. If someone put axle grease in there, you can use a big screwdriver and painstakingly pull out as much out through the fill hole the best that you can. It's a matter of dipping the screwdriver in and move it around until it is covered with grease, pull it out, wipe it off, "wash/rinse/repeat", and then fill it with Cornhead grease.
There will still be some axle grease in there, but it will mix nicely with the Cornhead grease and work fine.
I have just added some 90 weight oil to the axle grease in one to buy some time until I had time to rebuild the steering box. That helped.
