I tried around a bit this year with plastic repair. My aim was to try epoxy on my interior quarter panels on my 68 convertible, which are thouroughly broken on the edges and flanges but also on the flat surface over the years. So I bought 2-component-epoxy which you have to mix as described. For a stronger fix I decided to add glass-fiber-texture. You make one layer of epoxy with glass-fibre at a time (like a lasagne). Let the epoxy soak into the glass fibre and then the next layer. If you follow the instructions, it will perform exactly as described. First the epoxy is very liquid, then it develops through different "honey-stages" from liquid honey texture to heavy, creamy honey texture, then changing to sticky caramell until its hardening completely after about 20 hours. - You see from my descriptions I like to cook, too!
First picture shows the prep-state (1=quarter panel (always work from the backside), 2=glass-fibre cut to needs, epoxy mixed with a brush in a metal container (not plastic container - it can get hot when two components react with each other - and melt your mix container away - eventhough my mixture didn't warm up at all), 3=a metal weight to compress the panel on the work station). Please do wear those medicine gloves to protect your hands! It can get messy!
Second picture shows after-work-state (1=gloves!!!, 2=epoxy 2-component-mix, 3=glass fibre "lasagne" - multiple layers of glass fibre with epoxy mix softened and laid out in the broken areas). You see, I even repaired broken screw-counters which I could drill a hole in afterwards to receive the screw (#4).
If you take care of a good fixation for the epoxy to harden in, you'll get very good results with a very strong (as good as new) fix. You better work on the backside of the part to repair. Keep a good dis-adhesion (with baking paper or teflon spray for instance - which I didn't unfortunately) from anything which should not adhere to the part. Picture 3 shows my mess I received because I didn't realise the epoxy ran through to the bottom and I almost made an everlasting bond between my quarterpanels and the carton I placed to protect my working station. Only with a hot air blower (#1) I could ease the material a bit so to loose the carton (#3) from the quarterpanel (#2). That's your plan B if something goes wrong - a hot air blower will help you out. Anyway I'll have to repaint the quarter panel - so I could live with this mistake. I got rid of most of the carton from my quarterpanel. I even repaired the broken clips/buttons for the top boot cover which almost all tore out through the years.