Guys, thanks for taking the time to reply.
I find it hard to believe that there was a grp tabernacle, there is no sign of a previous grp attachment anywhere else. Also I did notice that the clearance around the mast at the foredeck (where the damage is) is much greater on mine than on the MK2 that I had a “familiarisation” lesson in, the mast would have to bend a hell of a lot to hit the screw heads. Even so I will certainly bear that clearance in mind when repairing.
However, as the boat is over 30 years old, anything could have happened to it!
The plot thickens……