Look up places that sell or fabricate using acrylic (plexiglass). They will have Methylene Chloride which is what is used to fuse acrylic, polycarb and ABS. Commonly sold as "Weld-on". Done properly the joint is stronger than the base plastic. The advantage of using this product is that it does not haze or leave the white residue like crazy glue does. The stuff is as thin as water so you can apply it from the back side and it will creep into the finest crack. Any excess evaporates - its a chemical, not an adhesive. You'll need to buy the applicator bottle and needles as well. Once the cracks are fix you could reinforce the area with some scrap abs (pulled from a wreck in a wrecking yard).