Kubota oil pumps will rarely wear out. I've never seen it happen.
Minimum allowed oil pressure at idle is pretty low on a Kubota. About 7 psi is the low limit. The standard oil alarm switch closes at .5 BAR / 7.25 psi.
Typically, the maximum oil pressure is controlled using a ball and spring release valve that is located at the oil filter
mount base. This valve opens at high pressure and dumps oil back into the pan. Remove the oil filter
and you should be able to see the ball in the seat at about 4 o'clock relative to the threaded stub. The spring is behind this ball. If this pressure release valve has trash in the seat and the ball is not seating and sealing correctly, you will see low oil pressure at lower RPMs. The problem will get worse as the oil heats up and gets thinner.
Remove the valve and clean it. The threaded stub must be removed to access the valve. Or you can try pushing the ball back and spraying some brake cleaner in there to remove any trash. Little slivers of plastic from the neck of an oil bottle seem to be the most common culprit here.