Do you know why it compressed? Was it the floor that failed and pushed downwards, is there a visible deformation of the hull under the water at that zone?
Or was it the post that shrank with the weight.
Absolutely yes, do repair with a shimming piece, but if you can, make a new compression post. I assume it's wood correct? Just make sure the shims are correctly secured and attached eithr to the post or the hull, so they don't come off as you sail and drop the mast all of a sudden which will cause a failure.
Yeah it looks like the plywood sole was softer than the compression post, and it "crushed" into the sole. There is no sign of rot at all. As far as the make up of the compression post... it's a two piece. The top half looks to be made of steel, the bottom half is wood.
I can't get the jack directly centered under the mast, but what I plan to do is loosen the turn buckles a little at a time and jack up the post / mast, and shim it with some aluminum plate. (I will take your advise and secure the shim, thanks). I think it is a feasable plan. We do not have crane service or drydock facilities yet, so I'm trying to address the issue in the water.
Your reply is very much appreciated, if you think of anything else let me know.