Mine did that exact same thing.
Do you actually use the roof rack? I tied something down just a tad too tight - and it cracked like that.
So I went to the local mazda stealership, and you wont believe the crazy ass prices they quoted. They told me one side was for $490 and the other side was $505. My jaw just dropped to the floor, so I decided to just buy the stock molding and purchase an aftermarket roof rack.
Here is a data sheet of all the pieces and part numbers.
Part# for stock molding without roof rack.
BJ3D-50-9H0E right
BJ3D-50-9L0E left
This also shows the window sills,side skirts and other stuff.
if you wanna sell lemme know ill grab the stock rack from ya