I have a small crack forming around the front of the fin box on the under side of the board. I was thinking of digging it out a little with the dremel and filling with it epoxy to re-seal the board, then keep a close eye on it. Hopefully there is nothing too bad underneath and the seal holds - otherwise I have some deeper surgery to do...

Has anyone done a similar repair or should I be taking this to a professional?

Cheers
Brett

that looks like a power box and my guess is its a tabou or simular fiberglass box , have a look at the top where the fin is bolted and see if there is any damage to the cavity

Agree with Decrepit - no water exiting the crack when left in the sun with the breather screw tightened, means no water has got in.
It looks so tiny (thin) as to be just a crack in the paint only, due to finbox movement on the smallest of scales.

On the other hand, I am inclined to fix things anyway

If so - drill a 1mm hole at the ends of the crack - this stops it going further.... 3-5mm deep holes should be plenty.
Grind out the crack with a thin cutting blade in a Dremel so you just have a cut in the board- or if you cant get one, a 40mm ish washer, with some cuts in the edge to rough it up, on a bolt in the drill will do. Be careful, we are talking a tiny cut.
Then fill with epoxy resin.

well I think it's probably a waste of time tying to fix it.
I'm fairly sure the crack is because of the poor bond between epoxy and the plastic the box is made from. there is a good bond to the side of the box because of the dovetail grooves there, but the front of the box is just straight plastic. Any flexing in the bottom sandwich will cause a hairline crack there. Your repair attempt may only last a few sails.

I guess if you can drill a few of small holes, in the front of the box, so that the holes are about 70% in the box and 30% in the foam that will act like the dovetail grooves in the side, and give a better bond, but you're still in danger of drilling thru any sealing that's there.

It's possible that I'm wrong and it's not a chinook box. If you scratch the paint behind the crack I predict you'll find black plastic.
If not and it looks more like fibreglass or carbon fibre, then a fix may be in order.

Some boards have a layer of cloth over the box, the crack is still there, but the layer of cloth covers it up so you don't see it.

I can see the whole fin box getting pulled out if theres some movement.I think it would be cheaper & easier to cut the box out & repair it properly now than ending up with a massive whole were your fin box used to be & then you lose your fin & box When it lets go when your sailing. Have fun

Yes i learnt about the two types of fin boxes the hard way the one that goes thought to the deck is whats in my board now the short box that only has post for screw is the one that ripped out of my board .Honestly i think if it was me & after ripping a box out i would have to pull it out & repair it just for peace of mind when sailing.
I cant understand why people are red thumbing the reply's to this thread .

Update: No water has come out of the crack (with plug sealed). so it looks like there hasn't been any leaks. The top deck where the fin bolts go also looks fine - cant see any cracks there. Might do a shallow repair just to smooth over the crack and if it returns take the board to a shop.

Cheers
Brett