My bike has always had one ugly broken fin, the top one, right side. Every time I look at the bike, it seems that's all I can see. Short of pulling the engine and swapping heads or having someone fill it properly, I've been trying to find something to at least fill it temporarily and make it look passable. In doing some searches, I came across a product called FIXIT, an epoxy-clay compound. Maker claims it will stick to anything and good up to 500oF.
You do the usual mix equal parts, in this case you knead it until the color is uniform. It can be formed for up to 3 hours, you can smooth it with a wet finger and needs very little support and completely solidifies in 24 hrs. Thought I would give it a try. It looks better and a bit more work would probably make it look more aesthetic, but I think I'll hold off until I see if it holds up to repeated heating/cooling an vibrations. Pics below.