I just replaced mine as well. There's no o-rings in the tube. The tube is not meant to be sealed. From my understanding there shouldn't be any pressure build up in that tube because it can cause stiffer steering, even hydraulic lock. The grease zerks that come with the boat actually don't have a check valve. This prevents pressure build up. The problem is most people loose the original grease fitting and replace it with one that has a check ball. (I had to) So what i do is, I grease the tube, then take the grease fitting back off and turn the wheel back and forth. Repeat once or twice, then put the fitting back on. Don't forget to grease the rudder assembly too. Hope this helps.
You don't have to buy a lake to own it~MasterCraft