This may be a total moron question, but we painted an old wood garage door with a paint that was not designed for exteriors. It's a custom colour that was left over from the previous owner and it looks GREAT.

Our concern is that since it wasn't made for exteriors it will degrade very quickly. (I've been told that the primary concern is UV protection.)

Is there a 'kleer koat' product we can paint -over- this to provide the same protection that a good exterior paint might do?

Or do we need to simply suck it up and re-paint with a proper exterior paint?