so I bought a double din dash kit for my 03 g35 for $30 there was a crack on the vent opening and by the time I got home the piece had completely broken off I have a friend that does plastic welding as it's called but wanted to try something I saw on YouTube. The video I watched you put baking soda on top of super glue and it dies and hardens it instantly and it's 20x harder than Normal they use it to fix chips on helicopter propellers. So I tried just super glue first and didn't even come close to holding it but than I remembered the video I saw a few months back I put the super glue a healthy amount on both sides on all 4 broken sides 2 at a time and then covered it with baking soda the results were amazing it's now as hard as a rock it actually feels stronger than the other side no joke and since the vent openings are set back you can't see where it's fused together. This trick can be used on anything plastic and the results will amaze you here are pics

You can chip off the excess as it will chip if enough pressure is applied without damaging the fixed piece but I didn't since you can't see it when installed

I could but you can't see it when installed and the excess will just chip off if you want but it's so strong right now I didn't want to take a chance of weakening it when you can't see it when installed but let me tell u it not only works it works better than I had even hoped