I spent yesterday evening, cutting out the bad bits and adding an extra piece to scarf up a new longer batten.
Balcotan PU is perfect for scarfing Oak. I have cut and glued a few test pieces, and tested them to destruction, and I laminated up a curved batten which I simply left around the garden. A year or so out in the weather seems to have done it no harm.
My scarfing jig had a minor problem, in that the battens were too thick, and my Circular Saw only cut 90% of the way through. I finished the job by hand and then planed it all smooth.
Once the glue is set, I'll bend it into place with a few clamps and make sure it runs fair.