Hey AusMoz, I'm in the camp of fixing the damaged base. Without making a mould you can rebuild a crumbled or broken ends, 40 or 80 grit sandpaper to rough the surface then use stiff plastic (from stationary shop) so it recreate the end for resin/fibre mix.
With the damaged fin, most probably damaged tip you can sand the tip and get a fin foil shape that will work and not spin out. It takes time but a great skill.
Send photos of your fins for better ideas