Performance Polymers Part No. 47809 or 22845 Plastic Welding System
I have used this product numerous times to repair cracked tupperware or replace tabs on my Honda ST. It is a two part plastic welding system. Just rough up the area around the surfaces to be repaired (the more rough area exposed, the better), wipe it down with lacquer thinner, and apply a liberal amount of this stuff (don't be stingy with it).
It turns as hard as the plastic and you can even carve away the excess later.
It is cheap too. I found my last tube at Autozone...less than $10 if I remember correctly.
G