Heater Box

Be careful with a heat gun, keep it moving to heat the whole area, not just one spot. Heat guns can destroy a part quite quickly if concentrated in one spot. Heat lamp can also be considered, but can also have the same problem. Your moving the whole area, not just one spot. If you need a sealer for the mating surface, get a roll of rope caulk sealer from the hardware store and make smaller bead to seal. J B weld can be used for cracks or small repairs.
Advice above is good.
Good luck