Use Milliput. It is a two part epoxy resin putty supplied in two sticks. Break off two lumps of equal size. Knead them together and press on to the part. It takes 24 hours to set and adheres to any substrate. Dries rock hard, can be filed and sanded smooth. It even sets under water. I have just completed a resin kit where I used it to fill gaps and to form a wing fillet. Brilliant stuff.