Over time the mast step for the mizzen wears, in extreme cases all the way through. The continual movement of the mizzen mast will slowly wear through the GRP, this must be a particular problem for a boat which is kept on a mooring. Even the mast support will contribute this erosion, as the boat is trailed.
To prevent this becoming a problem I decided to clean the socket and then add a small amount of resin and tissue. Finally a used a thin piece of polypropylene to prevent wear of the actual GRP. This was held in place with a small amount of glue and held down by the mast support while it dried. The final picture was taken before the mast support was put in place.