Quote Originally Posted by rubber duck View Post
Looking at the last set of photos with three screws, and provided I've understood what you've done correctly, I think the three screws that now secure the arm board cutout to the top plate may nullify the purpose of the cutout to break up vibration to the arm from the top plate. I think there are several ways to fix the sagging plinth that preserve the design aim of the cutout, e.g. on pink fish.
Thanks for the feedback. I searched on the Internet a few months ago and the only proposed solution I found was to bolt a metal shim below the top plinth and across the cut-out, to level the two parts and thus eliminate the sag. I did that initially, hence the six holes you can see on my deck. However then I realized that the horizontal screw across the two parts would provide less contact (and coupling) compared to the metal shim method.

Are you perhaps aware of any other method, which may be preferable?

Thanks for the feedback.