Some if the thin resin layer is peeling off. I've given it a good sanding, but it's far from perfect. I was thinking of brushing resin over the effected areas, then sanding/fairing flat. Does this sound about right? Or maybe I should just leave it?

I don't see much damage, looks like the final gloss coat has peeled off, either repaint it or just 400grit wet and dry it smooth

Hard to tell if there is actual delamanation of the carbon from these photos, but if there is only gloss coat pealing off its just improved the fin! Sand with 400 then 600 then 1200 then 1500 grit wet and dry very evenly and you will have an awesome fin again ... and it will even be shiny.

Yeah it's just the clear coat. Better off without it, adds weight ;) !

Board Lady has a page on fin repair, in case you need to:

boardlady.com/finrepair.htm

Brilliant, thanks all. It is just the thin gloss coating that's peeling. I'll give it a good sanding this week.

Use a block and sand chord-wise not length-wise.

It is most likely a clear Polyurethane coat. Sand it off with 400..be carefull not to go tto deep and into the carbon. Then just coat it with UV stable epoxy or clear polyurethane and sand it smooth..400 then 600.
Or maybe not even bother with the clear coat if it has come up OK after samding the clear off.

^^^ +1

Thanks every one. The peeling areas are at the base, tip and trailing edge. I think I'll do as Martin says, and coat the effected areas with clear Polyurethane, then sand to blend it in.

Thanks again