They don't need to be greased. The bearing is also captured by a snap ring, the bearing itself can be replaced easily. It's a military spec, and is impregnated with lubricant. I've put about 36K miles on a set through 2 winters with no dust sheilds and it's still like new. The bearing itself is common and inexpensive, the expensive part is the machine work for the sleeve and the housing.

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