So you need to do multiple layers and build up the part gradually. Assuming you start with a broken plastic piece, use a good fixture to hold the part, and cons

So you need to do multiple layers and build up the part gradually. Assuming you start with a broken plastic piece, use a good fixture to hold the part, and consider using a superglue activator spray on the plastic first. Then add as much superglue you can without dripping, and quickly sprinkle enough baking soda to saturate the super glue. Let it dry for a couple of minutes, dust off excess baking soda. Then alternate super glue layer, baking soda layer until you get slightly bigger than final shape. Let it cure fully and then sand it down. I've seen people mend hockey stick blades with it, so it can definitely hold up to a beating. It seems to be a little elastic, so lasts well as long as the bond to the underlying material is good.