There actually is no reason to add grease to these tie rods, since they are sealed units. If you cut one apart you will actually see that they have a plastic insert that acts like a lubricant - so there is no need to grease them. In many ways it makes the units more reliable to be sealed as they would not dry out that easy, or allow contaminents to enter into the tie rods. Many cars today are the same way with not having any zerk fittings on suspension components.