Do other J/28's have the zerk fittings? I'm guessing these were an after thought. It looks like you have a roller upper bearing, maybe a Harken on the post. The stainless sleeve you have on the post looks the same as the one that is used with lower roller bearings. Is it possible that the boat was built with a Harken lower bearing and that a previous owner wanted to to do a cheaper replacement and added the Delrin bearing and zerk fittings?
Paul L
Paul L