The part of the panel that cracks/breaks is made from styrene. You can use a judicious amount of MEK to melt the parts together from the back side, and then use some scrap styrene to reinforce the area with more MEK to melt the reinforcement to the back of the panel. Shape the styrene with a heat gun to match the curves of the panel. Do not touch the front of the panel while using MEK, or you will leave your finger print on the surface.
There is usually a small ridge where the repair is, because the liquified plastic oozes out a little. Allow it to dry for a couple of hours or over night. Go over it with a piece of Scotchbrite to remove the ridge after it has solidified.
You probably will have to paint the panel, because if you get any MEK on the front side, it will make the area shiny. The Scotchbrite will take the shine off for the most part.
Do this outside. MEK is nasty stuff.