Originally Posted by GuitarBob

I am not an expert, but I don't think any of the epoxies I have used would absorb water; again, I've used them to seal boats that are used in salt water. I don't know the formulation they use to make CF laminates, though, but I can't imagine it being much of an issue.

Keep in mind that what you're dealing with on the outside of that crank arm is epoxy (of some type). If I didn't like the flat look, I'd just polish the surface lightly until it got to where I liked it. I don't think you would affect the structural or long-term integrity in any way by adding a clear coat, just the appearance.

So far as the type of clear to use, you want to choose something that will stick to epoxy (I'm not sure if getting things to stick to epoxy is an issue, but it is for other bases, so be sure to check). I mostly spray lacquers, which I have sprayed over epoxy, but part of my standard finishing steps include spraying an isolator coat that anything sticks to (complete overkill here!). Again, I don't know how well things stick to epoxy directly -- it might be fine.

As suggested above, an auto paint-supply shop would have good answers for you and all the materials you could ever imagine.