google (and several beers) may be your friend as you learn a bit. Hopefully more than me as I screwed up several times ...
I *think* there are 2 very different methods for "gluing plastic". The first type "melts" the plastic and forms a chemical bond between the 2 pieces. The second type forms a "mechanical adhesive" between the 2 pieces.
My first adventure was trying to fix a Canon underwater housing. I used crazy glue and some random plastic. The crazy glue "crazed" but worked perfectly. It formed a chemical bond.
My next test with a very different need and was trying to adhere a polycarb block to a polycarb housing. Totally adhered, but did not fill gaps. So it was not waterproof. That was a SCIgrip acrylics 16 glue. This glue seemed to melt my blob and the housing (a bit) and attempted to bond them as 1. This did not work as the pieces did not fit together perfectly. oops! For the chemical bond you need the pieces to already fit perfectly.
The next test used the other stuff. E6000 Industrial Strength Adhesive. This stuck things together and filled all the little holes. But it formed a layer on top of the plastic. So it was no use for active pieces like the camera lock closure.
P.S. Try crazy glue on both sides...