One cause of fractured plastics is mis-aligned wireforms. If a wireform's
holddown fastener points are not well-aligned the playfield (that is, if you
have to force the wireform to fit by bending it), it can place stress on the
plastics around the fasteners and eventually cause them to fracture.
Carefully bend the wireforms so they install without placing any pressure or
stress on the playfield holddown points.