Final work belongs to the stroke over the panel edges. This will give closer impression to the light fall over the surface and better denote shape and structure. First you have to know from where is light coming. Then in regards to this you can make these highlights.
First create new layer and call it... see the image. This layer coming over last panel lines layer, never under!!! Make paths in very close distance to the panels and then make stroke path. For stroke path use brush, size 1-3 pixels, opacity 15% and color is white.
Final result is down there