ive never had a problem myself with cvh sumps and ive fit plenty but have heard of people having trouble
all i do is superglue the half moons to the sump a tiny blob of "curil" sealent on the corners of the moons and the rest of the gasket dry then tightened from the centre outwards and im yet to have one leak "touch wood!"
i would always use a genuine sump over non gen as ive found non gen sumps tend to not have a baffle in them