Some one on this forum recommended Plastex repair kits but I personally have not tried it.
http://www.plastex.net/Repaired_Photos.php
Tried using super glue and baking soda several time but it always broke. Was told it did not work because I did not use a expensive brand of super glue. If I was going to sped a lot on glue why not try something like Plastex or just replace the broken part?
But I have had good luck repairing cracks in hard plastic using cheap super glue.
It is a slow process of sanding and layering the super glue.