This one has taken me a bit to get to the bottom of, but I wanted to circle back around.
(much earlier in the thread I see I was talking in the plural, which I don't understand why because there is only one.).
I went through the rest of the season with no thruster, which was fine as it allowed me to hone my docking skills and significantly reduce my dependence on it. When I hauled the prop was in place and there was no growth or obstruction. Spinning the prop, you can 'feel' the differential turning in the pod.
I removed the bow thruster, realizing I could have done that in the water. The shear pin was intact.
There was a significant amount of carbon dust built up on the inside. I used an air compressor to blow out all of the carbon dust. This model has 4 brushes.
Two of the brushes had a significant amount of meat on them. They do not appear to freely move in the brush guides. The other two are so worn, that the springs are resting on the edge of the brush guides and can no longer push those two brushes down any longer.
judging by the difference in size, it appears that two of the brushes seized in the brush guides quite some time ago. The remaining two brushes are simply too worn and can't be pushed by the springs any longer.
I ordered a set of 4 brushes from Imtra. This looks like it will be an easy solution.