It is an epoxy based with powdered metal fillers. It dries hard so it is good for repairs where you need to fill a void and can be sanded, tapped, etc. But its very poor for anything flexable like plastic, it will just break away or crack. Proseal is more of a flexable, fuel resistant sealant. While it does act like an adhesive, its bond strenght is pretty low compared to a real adhesive. For your application, something rated for the type of plastic you are repairing will be better than either proseal or JBweld.