Initially, I pulled out the insert easily with a pick. It was an interference fit, albeit a bit loose. Upon installation, I staked the aluminum cover with a punch to prevent the check ball and insert from popping out. Theory is that at some point when the filter was being replaced, the spring pressure popped the insert out, and the ball was lost. When a previous owner put the spring back in and the insert, they might have not known about the check ball. Then when the engine was started, the oil light was illuminated. When they couldn't figure it out, they disconnected the oil switch, and the light was out.. Obviously not a good way to "fix" the issue. The mere fact that this engine survived this long is a testament to the Kubota design. I really don't think any damage was done to it. There was no glitter in the oil, and no weird noises to suggest bearing damage. A oil pressure reading will prove this. Next project is the glow plug system upgrade.