i don't see why you couldn't just use a piece of acrylic to patch it on the outside. just be sure to use the chemical bonding agent all the manufacturers use
my bad...i didn't realize it was a crack i thought it was a hole. and with that divider there it'd be hard to patch from the inside. i figured since there isn't much pressure being it's a sump that the exterior patch would suffice. am i wrong joe?