Good catch. As has been said here by several members lately, that particular bearing is easy to miss in routine inspections of the boat.
That's because viewing it requires determined contortions under the cockpit and a flashlight.
For the record, in the photo in Post #12, the machine screws are supposed to go through the flange, and the nuts then draw the bearing up snug against the underside of the cockpit floor.
If the bearing becomes loose, the rudder post wobbles. This can be observed under sail by removing the cockpit plate, when a wobbling post is obvious, especially when tacking. I had a top bearing so loose that the wobbling scored the underside of the cockpit plate.
A simple cockpit test of the security of the bearing is just to try to turn the four machine screws. They shouldn't turn easily. If they do, the nuts under the cockpit are loose. A loose top bearing can't be observed from the cockpit, because the plate itself doesn't move--only the bearing within.
Also: the grease fitting in the photo above looks rusted closed. They're hard to access anyhow. I just apply grease from the cockpit to the top of the rudder post, and it seems to ooze down sufficiently to do its job.