Your ventilation seals may be aging, but they have nothing to do with microwave energy leakage, (And microwave energy is not ionizing radiation anyway, so it does not cause cellular mutation or cancer)
You should check your grease filters (if you are venting to the outside) or your charcoal filter (if recirculating).
If you are venting outside, check your outside vent flap for proper operation, and check your outlet and ductwork for a bird's nest or mouse nest, etc.
If you have other questions, feel free to contact me directly, because FixYa doesn't always notify us when there are follow-ups.
- William E. Miller, AS-EET
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"