I've never had any flaking issues, but I am pretty careful prepping the fins if I know I want the edges polished. I've used normal 2k urethane, but normal spray can engine paint seems to be just as good on cylinders. After cleaning completely, usually glass bead, but the key to having a really good job is to polish the fins before you paint. I take a hand file and flatten and dress all the fins I want polished so they are nice and even with each other and of comparably thickness. This does not take much time and really makes a big difference. I take a paint stir stick and some 220 wet or dry paper and scuff up the top and bottom of the fins along the outside edge to make sure there will be great adhesion there. I don't think you need to fuss a lot deep in between the fins. Then I sand the edges I want polished with #600 and clean everything up and paint. Having filed the fins previously lets you use a block with the sandpaper. Once the paint is dry, it is an easy job to simply sand again the edges with the #600 to take the paint off. You'll get really crisp, sharp contrast between the bare edges and the paint, and no flaking at all. If you want the edges shinier, you can polish without fear of damaging the paint, but I usually leave the #600 grit finish - it is easy to renew the look down the road by simply hitting it again with the sandpaper.