Can anyone tell me how I can avoid this?

I want to design a part using the same
kind of metal - to - plastic interface as on
the Krups 203-70 coffee bean grinders but I
want to avoid the cracks in the corners.

If it gets posted it will be:
http://www.metalworking.com/dropbox/KrupsKrack.jpg
http://www.metalworking.com/dropbox/KrupsKrack.txt

Will this require say, a compliant adhesive
gasket between my metal surface and the
inside of the plastic reservoir or is this flaw
primarily caused by a different problem, say
a mixing issue that causes the plastic to be
really brittle?

Thanks!

--Winston