Old microwaves cannot leak radiation if they are properly maintained. This is because all these appliances are shielded and designed to contain the radiation within the unit. The radiation is confined to the inside of the unit by a steel-walled cavity, and there is a metal mesh screen that prevents the radiation from escaping. However, Health Canada warned that if the oven's door is damaged or if there is a large amount of dirt around the seal, the amount of leakage could increase. So it is essential to keep your oven door and seal clean and undamaged. As long as these safety features are working properly, there should be no risk of radiation leakage.