This is something we saw in some of the early Pro Anglers. The single countersunk screw wasn't sufficient and if the line was pulled real hard, or stored with it cleated down real tight, it would break through. We have since changed and are using two Truss heads. These have a big head on them and offer much more support for the block.
To repair this, you'll first want to remove the hardware you have. Drill a hole at each end of the crack to prevent spreading and then grind or melt open the crack a little to expose more surface area of the crack. Melt some plastic into the crack and fill it up. Sand it smooth when its cool.
You can trim a little plastic from the edge of one of your hatches to melt into the crack. A soldering iron or hot knife work great for melting the plastic. With the crack repaired, drill the hole back out, along with the second and install new hardware with big washers beneath them. Here's a photo of a repaired crack:
Let your nearest dealer know if you need any plastic and hardware. Screw 8031069 x2, washer 8080731 x2, nut 8050211 x2.
We also have a KC Welder Kit that works great.