I have worked on and heard of troubles with Moody rudders from the 1980s.
An advert was run in PBO by someone apparently trying to get others to assist him with a claim of some sort to do with a Moody rudder
I assisted with repairing a Moody 37 rudder where the filler had obviously been poured in with the rudder horizontal and the port side of the rudder had only a little filler and had filled with water
We carried out a repair about 10 years ago which is still working to this day.
I heard of an incident where rust appeared through the rudder and it was found that the welded on steel supports spreading the load from the rudder shaft to the blade area, were scrap mild steel off cuts and due to water ingress had rusted and the shaft could turn without the blade moving.
My suggestion which is what we did for the 37. would be to remove the screw and drill with an inch hole saw, slowly revealing the layers you drill through.
A plan can then be made to deal with the result.