I was about to post howto fix small plastic interior trims then found that you already have one listed here.
I got my Plastex from
-- HERE --.
They come in BLACK, CLEAR, WHITE, and other colours. The manufacturer mentions that Plastex kit in black is stronger than other colors. I used it to fix my turn signal but will soon fix some other cracks in my interior pieces too.
I started from enlarging the cracks by sanding them, using the smaller plastic tips to pour the plastic powder over the crack, then squirted the activator chemical over the powder. Pretty easy. There is also an instructional CD with movie clips to show you howto. The kit comes with small molding material that you could heat it up and mold small plastic parts.

After fixing the bulb housing, I sprayed my reflective dome with
-- Almost Chrome --