Looking at web pages, the Grampian 31 has a loyal following of owners. Not a lot of images. I found one that has a different looking mast base (appears to be wood).
Nice looking boat. Narrow at 8.4 feet. Definitely and old school vibe. Some of the boats appear to have been kit boats that were finished by the owners. Some have suffered from issues from water intrusion in their decks which results in some collapse or dimpling.
It appears from your image the base may be a cast aluminum piece.
You may need to remove the mast for a bit of time. Giving you access to the base.