The goose neck slide track had come loose and twisted last season. I took it off, to find that it was just held by four screws into the mast wall and some black mastic. Cleaned off all the gunge, filled the screw holes (which had enlarged, with thickened epoxy and then stuck a length of oak over the line of holes. I hollowed the back of the oak with a circular sander on the multi tool. Stuck it all down with a bed of thickened epoxy. I straightened the track in a vice quite easily and screwed the track back on.
The gap in the base of the sail track is to allow the sail slides to fit in, which they just do The whole thing is I hope much more robust now. There is a lot of lateral force on the goose neck in a strong wind and the original fixing was a bit slight.